Proceedings of the 7th International Conference on Concrete Repair, Rehabilitation and Retrofitting

The service life of a sewer is often set at around 100 years, regarded as a sufficient operational period without significant repairs being required. However, sewer concrete may experience severe deterioration, leading to structural and functional failures. 40% of failures can be attributed to biogenic acid corrosion, a chemical reaction between biologically produced sulfuric acid and concrete, leading to a loss of structural integrity and performance. Consequently, service life prediction models are needed for sewer management. Numerous models have been developed, but most remain ineffective and complex. The most common and widely used model is the Life Factor Method (LFM), but this model is limited when concrete with modern, high-performance binder systems and various reactive aggregates are used in different sewer environments. This paper presents further development of the LFM and applies it to predict the performance of different concrete mixes used for sewers in practice. The enhanced LFM model comprises sewer environment and material resistance factors, in which the environment factor evaluates the amount of acid produced on the exposed concrete surface in a sewer system, and the material resistance factor evaluates the amount of acid to be neutralised by the exposed concrete, considering the influence of binders and aggregates. Evaluating these two factors allows prediction of the corrosion rate of concrete with different binder/aggregate combinations when exposed to different sewer environments.

The need for sustainable rehabilitation (maintenance and repair) of existing structures is urgent and due to the expected deterioration of buildings and civil structures, there will be a great need for preventive and/ or curative interventions in the near future. More than 70% of the damage to reinforced concrete (RC), structures is linked to reinforcement corrosion, which can affect the durability of the structure and the residual load-bearing capacity. With the European transition towards a circular economy and the sustainable development goals in mind, it is important to deviate from considering only the technical requirements and initial costs during the design. Priority should be given to preserving products by extending their service life and prioritizing service life thinking. Therefore, the environmental impact and financial costs over the entire life cycle and the intended service life (SL) extension need to be considered. To assess the durability of RC structures and interventions throughout their life cycle, life cycle assessment (LCA) and life cycle cost analysis (LCCA) can be applied. For this reason, it is favourable to economically and environmentally optimize the intervention strategy for preventive maintenance and curative repair of corrosion-damaged RC structures (M&R strategies), based on a multi-criteria framework with the incorporation of LC(C) A. A residential building with damaged RC balconies in a Belgian coastal environment is chosen as case study. The objective is to assess five commonly used repair techniques environmentally and economically, i.e. patch repair, conventional repair, galvanic cathodic protection, impressed current cathodic protection, and total replacement. For a brief extension of the buildings’ SL (up to 5 years), patch repair emerges as the most favourable option, maintaining the existing condition with minimal intervention. However, to reach a longer SL extension (up to 40 years), conventional repair or cathodic protection emerge as competitive options where the entire renewal of concrete elements exhibits the highest overall environmental and financial impact.

The resistivity of concrete expresses its ability to conduct electrical current, which is carried by ions dissolved in the pore liquid. This is relevant for depassivation of embedded reinforcement by chloride transport, corrosion propagation and the application of electrochemical protection methods. Testing resistivity on existing structures may (i) reveal zones where corrosion initiation could occur early, due to high cover permeability and/or increased wetness, (ii) provide an indication of corrosion rate after depassivation, (iii) give information for defining zones in cathodic protection systems and (iv) help specify repair materials for matching resistivity with the parent concrete, as is required for cathodic protection. Several methods can be applied on site, for example non-destructive testing by means of a four-point electrode probe (Wenner probe), or destructive testing a.o. using a two electrode method on extracted cores.A set of RILEM Technical Recommendations published about 20 years ago is now under revision by the RILEM TC-OCM and the authors are members of the working group revising the Recommendation for On-site Resistivity Testing. This paper provides background, describes execution of on-site measurements using the four-point method and reports on experience in the field based on several cases in different countries, including measurement variability and the influences of exposure and concrete composition.

The use of performance-based design for achieving durable concrete structures is gaining traction across the world. The emphasis on linking concrete performance to the specific deterioration mechanisms has led to the incorporation of relevant durability testing in construction projects. However, there are several challenges in implementation of durability design strategies in the field, especially from the perspective of emerging economies like India. The objective of this paper is to highlight the important factors that come in the way of implementing durability design practices. There is a clear need for focused research that can help sort out such issues.

Operators and owners of roadways and airfields around the world spend a great deal of resources monitoring the condition of their pavements. Collection and analysis of these data are critical to predicting remaining service life, which is needed to plan future maintenance and rehabilitation activities. Understanding typical pavement service life is also important to the decision-making process for new pavement design and construction, including for activities such as life cycle cost analysis and life cycle assessment. Survival analysis is a statistical technique to analyze and model the expected amount of time before an event occurs. Widely-used in fields such as clinical medicine, epidemiology, and finance, researchers have also used survival analysis to study the performance of pavements and rehabilitation treatments. The survival life of a pavement may be defined in terms of time from construction until major rehabilitation or reconstruction, or time until various measures of pavement condition reach a critical performance threshold. This study provides a review of the literature of survival analysis applied to different types of concrete pavements and concrete pavement rehabilitation treatments, including concrete overlays. These analyses have used a variety of estimators to model concrete pavement service life, to investigate the sensitivity of concrete pavement performance to different design and construction parameters, and to compare the relative performance of different types of designs and rehabilitation treatments. The outcomes of these studies indicate that survival analysis is a useful tool for probabilistic estimation of concrete pavement service life and can provide useful insight into important factors in concrete pavement performance.

This paper presents a residual service life assessment of an offshore concrete structure for oil and gas production in the North Sea. After 15 years in operation, plans were initiated for a service life extension from 30 to 50 years, and a condition assessment of the concrete structure above the sea level was carried out. A probabilistic service life model based on Fick’s 2nd law of diffusion was used in the documentation of the residual service life of the concrete structure. The model parameters were adapted the actual structure, where the statistical data for the apparent diffusion coefficients and the surface concentrations were determined from concrete cores drilled out from the concrete above sea level. Using an acceptance limit of 10% probability for corrosion initiation, a service life of 50 years was obtained for the homogeneous, good quality concrete and a concrete cover in accordance with specified requirement of 50 mm + 20/− 0. Further, an updated service life analysis, based on chloride profiles determined 13 years later, indicated an even longer service life.

The Carinus Bridge is located at km 140.49 on Trunk Road 77/1 (R27) and crosses the Berg River estuary immediately south of Velddrif in the Western Cape, South Africa. Bridge inspections conducted principally by visual means, identified certain elements of the bridge that had deteriorated and has resulted in the bridge being classified as a highly critical structure. The most prominent defects relate to the half-joints in the central span (span 6) that has a drop-in element and is the longest span over the main river channel. Highways England’s CS 466 Risk Management and Structural Assessment of Concrete Half-joint Deck Structures was used to assess the primary risk. From this assessment, the half-joints on three corners were deemed a very high risk with the northwest corner being classified as immediate risk. This paper presents the findings from diagnostic tests performed at the existing bridge, with emphasis placed on the assessment of the exposure environment and reporting of environmental rate parameters that can be used for new reinforced concrete construction in the vicinity of the Berg River Estuary.

The reconstruction and upgrading of Trunk Road 11/1 (TR11/1, better known as the National Route N7) in Cape Town in the Western Cape necessitated the demolition of the Refinery Overpass Bridge B4247. This bridge had both insufficient vertical and horizontal clearance for the proposed widening of the N7. Furthermore, the existing precast beam-and-slab deck suffered from continuous vehicular impact damage over the years, resulting in continued costly repairs. This paper describes the condition of this bridge after a 58-year service life. The primary objective is to report and comment on the condition of this bridge in order for other engineers who have to rehabilitate, raise or widen similar bridges built during the same time, to have an indication of the quality of materials, workmanship, condition and behaviour. During and after the demolition operation, a visual inspection of the rubble was undertaken to evaluate the condition of this bridge which was constructed in 1965. Concrete cores taken before the demolition revealed higher concrete strengths of 50% and more, except for the precast beams concrete strengths which were well below the expected design strength after 58 years. Carbonation and durability tests done on concrete fragments indicated a robust and durable structure which would easily reach its intended 100-year design life.

Demonstrating the performance of a structural component is typically accomplished through calculations based on engineering models. However, advancements in material science have enabled the use of new materials in the construction industry. One example is fibre-reinforced concrete, which consists of concrete with short, discontinuous fibres dispersed throughout its volume to enhance performance under service limit states. The absence of conventional reinforcement can affect ductility and load capacity, making calculations alone insufficient to demonstrate the performance of these elements. Therefore, load-testing programs need to be developed. This paper reports and discusses the results of a full-scale test on a fibre-reinforced concrete multi-span slab-on-piles. The development of the test program, including the loading setup to achieve failure loads, is presented. The slab's performance is evaluated in terms of deflections and crack widths at various loading intervals corresponding to both service limit states and ultimate limit states.

The Herøysunds bridge on the west-coast in Nordland Fylke in Norway had undergone concrete repair works with focus on reinforcement corrosion. During these actions, it was discovered that the tendon ducts had loss of injection.To ensure the safety of the bridge it was decided to map voids and defects in the ducts. Several risk areas were pointed out by the contractor and a non-destructive test (NDT) was carried out. The scope of the NDT inspection was to determine voids in the cable ducts at the areas which had been pointed out by the designer. In the project we followed a strict procedure. Based on this we used a combination of different methods such as GPR (Ground Penetrating Radar), UPE (Ultra Pulse Echo) and IE (Impact Echo). It should be mentioned that considerable experience is needed when these methods are combined to investigate voids and defects in tendon ducts. In addition, it is difficult to determine the degree of grouting in the duct and the NDT methods often need to be combined with partly destructive testing, i.e. a hole needs to be drilled into the duct and closer investigation with for example endoscope might be needed. The results from the NDT investigate shows that the suggested approach was successful and it was possible with high accuracy to detect voids in the ducts. The methodology forms a basis for the procedure recommended by the Norwegian Public Roads Administration.

The 2011 Canterbury earthquake in New Zealand motivated a revision and enhanced standardization of protocols for the assessment of the earthquake risk of existing buildings across the country. The resulting document arising after significant consultation and discussion is the 2017 publication “The Seismic Assessment of Existing Buildings Technical Guidelines for Engineering Assessments”. The document provides guidelines on determining whether a building should be rehabilitated after an earthquake. This article is written primarily with the objective of providing a notion of how seismic assessment practice has changed in New Zealand since the Canterbury earthquakes in the context of these new technical guidelines. The procedures within the ISA (Initial Seismic assessment) and DSA (Detailed Seismic Assessment) are discussed. Two cases of the assessments being applied are then presented, the first example being that of a four-story reinforced concrete building in Auckland, an area of relative low seismicity, and the second example which is a four-story reinforced concrete building in Wellington, an area of very high seismicity.

To investigate the potential correlation between damage parameters used to assess the level of alkali silica reaction (ASR) in concrete and the mechanical properties of the material is a promising approach. Currently, ASR damage evaluation of concrete is done following FHWA protocol [1]. The actual level of damage (diagnosis) is evaluated using the Stiffness Damage Test (SDT) and the Damage Rating Index (DRI). Both methods provide parameters correlated to the concrete's expansion level. In addition, future potential of damage (prognosis) is assessed using residual expansion tests in specific climatic conditions (R.H. > 95% and T = 38 ±°C) and alkaline solution (NaOH 1N, 38 ±°C). Expansion is thus currently used to assess the damage and predict future deterioration. However, only expansion measurements are insufficient for infrastructure managers who need to understand the structural impact of ASR on concrete structures. Therefore, this research aims to identify new correlations between the actual test results and structural parameters of the concrete, providing more relevant information for infrastructure management. In this project, cores from ASR-affected bridges were extracted, cut into samples and subjected to both prognosis and diagnosis tests, as well as compressive tests, directly after extraction and after expansion tests, respectively. A linear trend was identified for compressive strength, correlating with DRI values in cores tested after extraction, indirectly linking to the concrete's expansion level. Young's modulus also decreased with additional expansion during the tests, but no significant trendline was identified.

The condition assessment of concrete sleepers poses a challenge for the South African rail network for two primary reasons: the scale at which measurements need to be conducted and the presence of ballast stone, which obstructs direct access to the sleepers for visual and non-destructive assessment. Literature related to common concrete sleeper defects and methods of condition assessment was reviewed. Literature was used to assess which of the concrete sleeper functional requirements a specific defect will inhibit or prohibit. A Failure Mode and Effect Analysis (FMEA) showed the severity of the concrete sleeper defects, their frequency of occurrence, and the quality of information provided by each of the condition assessment methods. The Residual Profile Number (RPN) from the FMEA showed which defects presented the highest unmitigated risks to continued rail operations. The top two most critical sleeper defects, longitudinal cracking and vertical cracks at the rail seat, are related to assessment methods that allow for maintenance planning requirements. Sleeper body abrasion was found to be the only defect that is currently not related to a method for detecting the condition well enough to sufficiently mitigate the residual risk to continued network operations. Methods that assess sleeper body abrasion need to be improved to meet maintenance planning requirements.

Corrosion of steel reinforcement is a main deterioration mechanism for reinforced concrete structures in the marine environment, where chloride ingress may cause severe and widespread damage. For infrastructure owners, an improved understanding of the particular environment can lead to the design of more durable structures, or the improved maintenance of existing structures, both leading to more effective investment decisions. The objective of this research were to perform as-built data collection, visual condition assessments and cover measurements on various reinforced concrete structures in the port of Cape Town, with the aim of drawing correlations between the parameters of marine exposure, cover depth, and age of structure to the damage rating related to chloride-induced corrosion.

Sensing technology using magnetism and IoT technology ‘SenrigaN’ is a non-destructive testing technology currently under development. SenrigaN is a solution that visualizes fracture of internal PC steel wires in concrete structures in real time. By analyzing magnetic data using magnetic sensing and IoT, it is possible to instantly find fracture locations on-site bridges. At the same time, it is necessary to appropriately find whether PC steel wires are fractured. In this study, we used Magnetic Flux Leakage method and using a 3-axis magnetic measurement device to automatically capture the characteristics of changes in the magnetic flux waveform when steel inside concrete breaks and built a model that finds the presence or absence of a break.

When devising plans for repairing and reinforcing concrete structures after a fire, one must evaluate the effects of heat on concrete. When a fire occurs in a concrete structure, the moisture contained within it evaporates owing to high temperatures. The authors investigated methods to assess the effect of heat by correlating the drying process during a fire with the heating temperature. In this study, a method for evaluating the drying degree of concrete after fire exposure was examined by measuring the electrical resistance, which is closely related to the moisture content of concrete. Initially, a method was investigated to measure the electrical resistance in the depth direction from the surface of fire-damaged concrete. Subsequently, the electrical resistance of the specimens heated to simulate fire conditions was measured, and the relationships among the electrical resistance, moisture content, and heating temperature were compared. Measuring the electrical resistance of the surface of concrete damaged by fire and then comparing it to the resistance of unheated concrete allows one to identify the area that had been heated to 150 ℃ or more and became almost completely dry.

Cathodic protection (CP) has proven to be an effective technique to stop corrosion of reinforcement in concrete elements and extend their service life. Although CP systems are more frequently used in Belgium the past decade, there still is an experience gap within the repair market with respect to this promising and effective electro-chemical repair technique. Different stakeholders within the (Belgian) (concrete) renovation sector must be able to interact with CP systems in order to increase their knowledge and experience with the technique. To achieve this, six reinforced concrete demo-panels were developed and stored in an outdoor Belgian sheltered environment in order to acquire a certain degree of corrosion. Different types of CP systems are installed on/in the concrete demo-panels. The different systems are monitored (e.g. corrosion current density, internal relative humidity, temperature, corrosion potential of the steel and protective current) through a remote sensing and control monitoring system. In this paper, the design of the demo-wall is presented and discussed. The start-up phase of the CP systems was analyzed and a first 24-h depolarization measurement was performed. Finally, the first two weeks of data generated by the monitoring system is discussed.

Hybrid cathodic protection (HCP) of steel in concrete works by combining impressed current cathodic protection (ICCP) and galvanic cathodic protection (GCP) into two consecutive phases. Hereby, the first phase (ICCP) aims to realize pit-realkalisation, while the second phase (GCP) aims to keep the passivity of the reinforcement. In this research, the influence of chloride concentration, cement type, charge density during first phase and type of anode on the throwing power and protection degree of HCP with discrete anodes is investigated for concrete slab elements. Results show a comparable throwing power (around 250 ± 30 mm) of the HCP system for concrete with no or a limited mixed-in chloride concentration and a varying cement type, charge density during 1st phase or type of anode. For concrete with a severe contamination of chlorides (2 m% Cl−  ~ cement mass), the throwing power is greatly reduced to only 50 mm. Consequently, based on the 100 mV depolarization criterium (EN ISO 12696:2022), HCP was found to be most effective for concrete with a relatively limited mixed-in chloride content and with discrete anodes containing an integrated DC power source.

Cathodic protection (CP) designs are crucial for the successful implementation of fully functional cathodic protection systems. Over the past 30 years, significant experience has accumulated in The Netherlands with the application of CP to concrete structures, leading to the establishment of a well-structured supply chain based on ISO 12696. This has facilitated mainstream implementation of CP. The accumulated experiences have resulted in a recommended practice, CUR Recommendation Cathodic Protection of steel in concrete, which is widely adopted in the supply chain. Most contracting companies have also implemented standard operating procedures, installation guidelines and quality control systems that align with the ISO standard and the CUR Recommendation. Those contractors routinely develop project-specific work plans with consistency and ease. However, large asset managers such as Rijkswaterstaat (Department of Transport) and companies operating power plants, who own multiple CP systems installed by different contractors over a period of two decades, have noted a significant variation in execution method, control, data acquisition and monitoring. This variation is undesirable from an asset management point of view, leading to a need for further standardization. This paper evaluates the process of generalizing specific CP specifications and emphasizes the necessity of modifying these general specifications to project-specific CP system designs to meet the unique needs of each project. This paper evaluates the process of (i) generalizing CP sketch designs for a select number of simple but frequently occurring cases, which (ii) then can be elaborated into project-specific CP system designs to meet the unique needs of each project. The first step of generalization will be done by an expert, while the elaboration can be done by a senior technician. The paper will also highlight key areas of focus in this process. The aim is to contribute to the ongoing efforts towards standardization, thereby minimizing the number of variables and enhancing the efficiency of CP system implementation.

Electrically conductive coatings have been applied for cathodic protection (CP) of steel in concrete with varying success since 1989. Principal challenges to long-term performance and reliability proved to be oxidation of the electrically conductive pigment and the acid produced at the anode/concrete interface during the operation of the conductive coating in the anode mode. Oxidation will lead to loss of electrical conductivity, and the anodic acid produced leads to delamination of the conductive coating. Both processes lead to the loss of cathodic corrosion protection. By using appropriate graphite pigments, oxidation is negligible, as was shown in an extended R&D project conducted from 2012 to 2015 by IBAC (RWTH Aachen, Germany) and BAM (Berlin, Germany). The detrimental effects of acid production at the anode/concrete interface proved to be more challenging to overcome. One successful concept was the creation of an acid-resistant micro-capillary matrix at and near the anode/concrete interface, which was applied for the first time in 1998 at a parking deck in Oslo. The concept of the micro-capillary matrix is based on the formation of a micro-capillary matrix by impregnation of the concrete adjacent to the anode/concrete interface with an alumo-silicate binder that forms acid-resistant zeolite-like structures that act as a sponge that pulls the alkaline concrete pore solution towards the anode/concrete interface neutralizing the anodically produced acid. Evaluation of laboratory scale probes by ESEM/RDX revealed the formation of zeolite-like structures in the concrete pore space; references are cited in the paper. Electrochemical evaluation proved that long-term current densities of 35 mA/m2 and short-term current densities of >100 mA/m2 are supported without loss of performance. Since 1998, the CAS Composite Anode has been applied in 96 projects protecting the steel in concrete in parking decks, road and highway bridges, seaside apartment buildings, concrete basins of swimming pools, concrete retaining walls, and marine civil structures. Performance data of laboratory scale evaluations and examples, as well as performance data of selected field projects in the Netherlands (parking decks, seaside apartment buildings) and Germany (parking decks), are presented.

Engineered cementitious composites (ECCs) have been established as a feasible option for repairing structures that no longer meet safety and serviceability standards. However, the large quantities of cement used in the composite resulting in a high carbon footprint and the high material cost associated with polyvinyl alcohol (PVA) fibers make improvements essential for a broader application. In this study, modified mix designs of ECCs were investigated using supplementary cementitious materials (limestone and metakaolin) to replace up to 70% of OPC and 100% of fly ash in combination with substituting PVA fibers with polypropylene (PP) fibers. As part of a broader study, the mechanical behavior of these mixes was examined by four-point bending tests and uniaxial tension tests and compared to the standard M45-ECC. It could be observed that as cement content is reduced, there is no significant additional loss of mechanical properties by simultaneously replacing PVA fibers with more cost-efficient PP fibers. The developed mix designs retain a high tensile strain capacity and tensile strength while enhancing sustainability and lowering the cost of the material. The results of this study present a promising approach to promote a broader application of ECCs in infrastructure repair.

Sugarcane bagasse ash sand (SBAS), a by-product of sugar and ethanol industries, can be used as a partial replacement of natural sand in production of eco-efficient concrete and mortars. Due to its finer particles, incorporation of SBAS results in refinement of pores in cementitious composites. This in turn leads to greater cracking susceptibility triggered by self-desiccation processes in autogenous shrinkage. To mitigate this problem, superabsorbent polymers (SAP) can be used as internal curing agents. This study aims to evaluate autogenous shrinkage and mechanical properties of cementitious composites with SBAS modified by SAP. Mortars were produced with 30% SBAS, and three types of SAP with different water absorption capacities. The results indicate high efficiency of SAP in controlling water supply for cement hydration, reducing autogenous shrinkage by up to 67% in relation to the reference mixture without SAP and SBAS. Flexural and compressive strengths were not significantly affected by SAP when compared to the reference samples. Therefore, application of SAP in such composites could notably improve durability of eco-efficient concretes.

Today, a vast number of existing concrete structures are reaching or have reached the end of their expected service life. With 50–80% of the concrete deterioration contributed to reinforcement corrosion, the demand for repair mortars is high. Compounded by a two-to-three-times higher cement factor, a pressing need emerges for developing sustainable and durable repair mortars. Sustainability can be considered by incorporating the environmental and economic impact over the product life cycle, and durability can be incorporated by technical performance. The focus of this study lies on electrical resistivity in which four hydraulic bonded and commercially available repair mortars were selected and exposed to three environmental conditions. Recognising the pivotal role of resistivity in applying cathodic protection (CP), EN12696 emphasises that the repair mortar’s resistivity has to be 0.5-to-2-times that of the parent concrete to have a uniform power distribution. To select compatible products, this paper aims to elucidate the correlation between distinct resistivity measurement methods (e.g. Wenner probe, TEM-external plates and TEM-embedded pins) while sample dimensions, sample origin, saturation degree and exposure conditions varied. Understanding this critical property is vital in the CP performance for service life extension of reinforced concrete structures. By integrating technical performance and environmental considerations, this research contributes to the ongoing development of sustainable and durable repair mortars.

The cementitious plaster applied to the facades of most buildings on upper campus of the University of Cape Town (UCT) has frequently been observed to fail with re-applications indicating repeated and ongoing failure. The UCT Plaster (or University Plaster, Lutyens Plaster) specification is a unique dash-finished plaster applied to many of the university’s buildings, some dating back to the 1920s, giving the plaster heritage significance. The observed failure is predominantly related to friability, delamination and spalling. Complementing this failure, there is a high variation in the plaster’s performance, appearance, and composition across buildings on campus. Investigations have shown the plaster specification to be outdated, with specific problems relating to detrimental old-fashioned colouring techniques and a lack of consideration for building materials available nowadays. Additional problems identified relate to substandard plastering workmanship and a lack of standardization. Repeating failure of the plaster results in negative social, environmental, reputational, and economic impacts for UCT. Therefore, a new specification is required, mitigating these failures and promoting standardization within heritage requirements concerning colour and texture of the plaster. Performance requirements were established in terms of fresh plaster workability, friability, bond strength, colour, and texture. A lab investigation included mix optimization and testing of workability, abrasion resistance, and bond strength, as well as visual aesthetic comparison tests. Tests were conducted on mixes with varying contents of cement, hydrated lime, sand, bonding admixture, and air entrainer. The findings show that, out of the mixes developed, a standard plastering mix and a separate finish coat mix using commercial pigments performed the best in context, provided adequate workmanship was applied.

Structural repairs are meant to restore or increase the load-bearing capacity of a member. The only way this can be done is for the repair to contribute and withstand the loads applied. Whether this can be done depends on the properties of the chosen repair material. The elastic modulus and compressive strength are often viewed as the most critical characteristics since the compressive strength ensures the repair can withstand the stresses applied, while the elastic modulus determines the structural contribution of the repair. However, little attention is given to other long-term deformation characteristics, such as creep and shrinkage. Studies on the structural contribution of repairs to axially loaded members typically focus on the repair’s contribution at ultimate failure but do not focus on the contribution in the long term under service loads. This paper presents experimental work on the influence of shrinkage and creep of cementitious materials on repairs subjected to compressive axial loads. The paper describes the experimental work conducted, where unreinforced concrete prisms were exposed to shrinkage before the cross-section was partially replaced with a repair mortar or concrete and axially loaded after three days. Strains of the repaired section and concrete substrate over time are presented, and the effects of creep and shrinkage in the repair on the composite response to axial loading are discussed.

In this paper the main considerable points for the material decision (resin, cement lime or grout) for a successful foundation repair were presented. Based on in-situ experiences from more than 70 successful foundation repairs in the past 8 years, the correlation between material behaviors and size, position and general condition of the cracks and cavities in a foundation will be explained. Doubts regarding the classic understanding of filling/injecting of cracks will be clearer. Furthermore, the method including preparatory actions to inject the material successful into the right position in the foundation will be shown.

The present study investigated the performance of non-seismically detailed beam- column joint (BCJ) retrofitted with high-performance hybrid fiber reinforced cement composite (HP-FRC) under quasi static reverse cyclic loading. A total of 20 mixes were developed to attain the strength more than 100 MPa. The mix prepared with the addition of 2% hybrid fibers (1% crimped and 1% hooked fiber by volume of mix) attained the 105 MPa at 28 days of water curing. The BCJ specimens were initially damaged at two different stress levels i.e., moderate and severe damage levels. The results obtained in reference specimen was compared with its retrofitted specimens in terms of hysteresis curve, energy dissipation capacity, stiffness variation, and joint stresses. The overall performance of the specimen retrofitting with HP-FRC was improved. The decrease in initial damage level increased the efficacy of HP-FRC in improving the seismic performance of retrofitted BCJ. Further, the hooked steel fibers assisted in regaining the original strength and negating the spalling of concrete during ultimate failure. The secant stiffness variation also displayed that the retrofitted specimen helped in improving the stiffness of joint.

Alkali-silica reaction (ASR) is among the most common forms of concrete degradation. The reaction leads to expansion and cracking, which can decrease mechanical properties and increase permeability, leading to loss of service life. Confinement is one method to limit the expansion caused by ASR. Ultra-high performance concrete (UHPC) exhibits superior mechanical properties but its use as a repair material for the confinement of ASR-affected concrete elements has not been well-explored. To fill this gap, an ongoing experimental, modeling and monitoring effort is investigating confinement of ASR-damaged unreinforced and reinforced concrete (RC) columns. Laboratory-cast, large-scale rectangular and circular columns were stored an accelerating environment at ~ 32 ℃ and ~ 99%RH, with expansion monitored over time through internal and external strain gages. Once an expansion of ~ 0.1% was reached in some samples and surface-breaking cracks were apparent, repairs were undertaken. This paper describes the application of a continuous 3-inch-thick layer of UHPC around a rectangular RC and a circular unreinforced column. The design was informed by an initial ANSYS finite element analysis (FEA) model. Although this work remains ongoing, this paper presents designs on the concrete mixture design, reinforcement detailing, ASR damage, approach to confinement design, confinement application, and monitoring.

The preservation of existing bridges, many of which were constructed over 50 years ago, is crucial for the future development of road networks in many Western countries. These bridges often fail to meet modern loading requirements and seismic resistance standards, affecting their operability and safety. Current regulations emphasize cataloguing existing bridges and identifying critical structures in need of structural rehabilitation. Among various intervention techniques, the use of fiber-reinforced concrete (FRC), particularly high-performance fiber-reinforced concrete (HPFRC), is gaining popularity due to its superior performance, application speed, and simplicity. This paper presents the results of an EU-funded project focused on the repair of two road bridges in Italy using HPFRC. The successful implementation involved applying jacketing to the bridge piers and girders, which were heavily damaged by corrosion, using a new HPFRC layer with a reduced thickness of 40–60 mm and limited steel reinforcement. Laboratory tests conducted at the University of Brescia on scaled column specimens yielded promising results, showing an increase in the load-bearing capacity of the columns under lateral loading by up to 100%, with moderate effects on the stiffness of the existing structure. The paper suggests that although HPFRC has demonstrated significant structural benefits, its broader environmental implications must be considered.

Rapid-setting binders such as Belitic Calcium Sulfoaluminate (BCSA) are increasingly in demand as the need for rehabilitation and fast return to service of roads, bridges, and airport pavement grows. Speed of construction, low shrinkage, and low carbon footprint are the key features of BCSA concrete. The binder was first developed in the United States in the mid-seventies. It allows concrete infrastructure to be replaced and returned to service within hours. BCSA concrete slabs placed at the Seattle International Airport (SEA) in the 1990s are still in service 20 years later and have doubled in strength. BCSA concrete placed on California freeways has tripled in strength in 25 years. The binder also allows innovation in pavement and concrete design. BCSA is also the basis for the design of various rapid-setting performance-engineered concretes, such as Portland-Limestone Cement (PLC) and Limestone Calcined Clay (LC3) concrete with enhanced early strength. This paper reviews recent concrete applications based on BCSA cement and the opportunities they offer in building a more resilient, lower-carbon concrete infrastructure. We also discuss durability and standard specifications.

Fibres have long been added to concrete to enhance its post-cracking ductility, toughness, and to control the propagation of cracks in fibre reinforced concrete. The random dispersion of fibres in the composite improves crack control since the location and growth directions of the cracks are random, and the fibres are dispersed throughout the concrete matrix. Applications of FRC include pavements, bridge decks, and tunnels, among others, all of which may be subjected to various types of loading throughout their service lives. These loadings may occur as static or fatigue loadings. The fatigue behaviour of FRC has been explored by several researchers to understand the response of FRC to fatigue loading. However, the focus has been on the uncracked state, which does not assess the post-cracking capability of the composite, which ultimately determines the remaining service life of the structure. This research investigates the fatigue behaviour of pre-cracked steel and polypropylene FRC at various fibre dosages. Two hooked-end steel fibres were investigated, namely Dramix 3D-65/60-BG and 5D-65/60/-BG. The polypropylene fibre used was Masterfiber 240. The results show that the fibre type is the leading cause of premature failure. Stiffer fibres such as steel fibres are able to provide improved post-cracking ductility compared to polypropylene. Furthermore, to enhance the post-cracking ductility, more fibres are needed to bridge the crack, and consequently, an increase in fibre dosage resulted in improved fatigue behaviour.

This research investigates sustainable construction practices and life cycle assessment (LCA) in repairing and strengthening concrete bridges. The study emphasizes the importance of minimizing environmental impact while maintaining structural integrity and functionality. Sustainable approaches are discussed, and the role of LCA in evaluating and comparing the environmental impact of different repair options is highlighted. Combining these approaches, the research presents a framework for environmentally responsible bridge repair practices that enhance sustainability and performance. The findings underscore the potential for significant environmental benefits by adopting innovative and recycled materials and low-impact repair techniques, all assessed via comprehensive LCA methodologies.

Fire incidents due to the increased road transportation of flammable materials are a concern for steel reinforced concrete road bridges and allied structures. Though these structures are more fire resistant than steel bridges, they do require a more detailed consideration in the provision of fire safety measures as design considerations and post-fire exposure response. This study presents a comprehensive examination of the structural damage and subsequent rehabilitation of the B112 Sarnia Road Grade Separation Bridge on National Route N2, following a severe fire incident resulting from the collision of petrol and diesel tankers in August 2015. The bridge sustained significant fire-induced damage, manifesting as concrete spalling and visible cracking. Through an extensive damage assessment, including visual inspections, ground penetrating radar (GPR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and thermal imagery, the severity of the damage was evaluated. The fire-induced damage was seen predominantly in the concrete matrix, with observations of spalling, a change in colour indicative of high-temperature exposure, and microstructural alterations. This case study further presents the details of the access system considerations, repair objectives, methodologies, and performance testing, ultimately demonstrating that careful monitoring and a well-executed repair response can significantly extend the service life of fire-damaged structures and ensure future serviceability.

The Ordinary Portland Cement (OPC) is engineered using the agro waste derived graphene oxide (GO). GO was prepared from rice husk through phosphoric acid activation. The prepared GO was added into OPC at different weight ratio to study its impact on the mechanical properties. The functional groups, morphology and composition of the composites were studied using FTIR, SEM, and EDAX. Experimental results indicated that GO was dispersed in OPC composite. The mechanical properties of GO added OPC composites were studied. The results revealed that GO added cement composite shows relatively higher compressive strength compared to GO free OPC. Moreover, the compressive strength of OPC composite increased with GO content up to 0.04 wt.% and slightly decreased for the composite with 0.06 wt.% of GO. Hence, the prepared OPC composite with 0.04 wt.% GO was practically applied in rehabilitation and strengthening of a monumental building. An ancient temple has truncated pyramidal stone masonry tower with a brick masonry vault above. Lime mortar is used as binder. It is rehabilated and strengthened using the agro-waste derived GO-based OPC paste, corrosion resistant steel bars and meshes for strength and confinement. Brick masonry vault is given surface treatment and finishes with prepared composite. The results support to cure the damages in the monumental buildings and to preserve heritage.

The work reported in this paper is part of a study intended to assess the long-term performance of surface repairs that were carried out on reinforced concrete elements of the Champlain Bridge (Canada), recently decommissioned after 60 years in service. The dismantled bridge has provided unique real-size specimens exposed to severe weathering, including freeze-thaw cycles and de-icing salts. Among these, repaired infill slabs and prismatic sections of a main pier were selected to conduct an in-depth evaluation of bond and cracking. The results reveal that while some repairs exhibited variable bond strength and some cracking, they overall performed satisfactorily. This study highlights the critical role of material selection and repair techniques in prolonging the life of concrete structures under harsh conditions.

This paper presents the extension of life for the vent shaft at the Wessels Manganese mine in Hotazel, Northern Cape, South Africa. The existing vent shaft comprises a concrete box-type structure sloped at 6% to allow vehicle access to the underground operation in emergencies. In addition, the vent shaft supplies vital air to the mine, thus closing of the shaft is not possible. The new rail balloon intersects the shaft perpendicularly, on a fill of 10 m. The existing vent shaft was constructed using low-strength concrete with mild steel reinforcement bars that were available at the time of construction and therefore does not have the required structural integrity to carry the fill and associated rail loading. Several options were evaluated to extend the service life of the vent shaft, including building a bridge over the shaft and constructing a new vent shaft that would daylight at a different location. The most feasible solution was to keep as much as possible of the existing vent shaft and construct new sections under the high-fill regions. Rapid impact compaction was required on the collapsible in-situ soil conditions. To ensure uninterrupted air supply, a collar was introduced over a section of the existing shaft, equipped with a chimney to serve as temporary air vents. This allowed for the upper portion of the shaft to be demolished and rebuilt, thereby extending the structure’s service life. Additionally, wing walls were constructed at both the top and bottom to prevent the new rail fill from encroaching on the remaining portions of the old vent shaft.

In reinforced concrete, the carbonation of the concrete cover can lead to the loss of passivation of the reinforcing steel. As a consequence, steel corrosion might occur. The current trend to concretes with reduced clinker content, often in combination with pozzolanic substances, increases the risks for damage due to carbonation, as the Portlandite content in the concrete is reduced significantly. This is an important limiting factor for the quantities of calcined clays that can be used in concrete. For this reason, it was investigated whether an increase in the Portlandite buffer could improve the carbonation resistance. The basic suitability of this approach was confirmed. This should make it possible to increase the clinker replacement rate with supplementary cementitious materials. Furthermore, an alternative approach based on a binder with γ-C2S was investigated. This usually inert phase reacts with atmospheric CO2 and moisture, forming additional phases. This effect was found to densify the concrete surface to such an extent, that an extremely high carbonation resistance was achieved. Furthermore, the densification also increases the resistance against chloride ingress. The incorporation of γ-C2S could thus help to achieve a good durability for low carbon concretes.

It has been important to comprehend the transport mechanisms of aggressive ions in concrete for an approach based on performance and durability indicators of reinforced concrete. Chloride ions can cause corrosion of reinforcing steel in concrete and as result of causing severe degradation of reinforced concrete structures. Besides that, chloride migration coefficient values have revealed as an interesting parameter and indicator of durability of concrete exposed to chloride-rich atmospheres such as marine environments. Thus, this paper shows a mini-review about some test methods for experimental determination of resistance to chloride penetration in cement-based materials. Some of them methods were listed, summarized and categorized as chloride diffusion coefficient or chloride migration coefficient and as in steady state, non-steady state or multi-regime state. In addition, the advantages and disadvantages of these test methods have been mentioned within the context of a general discussion of them. Finally, the chloride diffusion/migration coefficients have been used as input parameters in service life predictive models to evaluate and guarantee durability for concrete structures in marine environments.

Shrinkage cracks in concrete often start to form in the first few hours after concreting. These shrinkage cracks accelerate both carbonation and direct corrosion of the reinforcing steel. By adding fibers to the concrete matrix, it is possible to reduce the early shrinkage cracks. However, the effect of the fibers on the characteristics, as well as the number of cracks depends on many fiber-specific factors, which make a quantifiable prediction almost impossible.By adjusting the environmental conditions in the laboratory to achieve a very high evaporation rate, it is possible to generate shrinkage cracks and thus obtain a comparison between fiber-reinforced and non-reinforced concrete profiles. Suitable geometric and physical parameters for conducting a shrinkage test in a wind tunnel were defined more than 40 years ago. At the University of Applied Sciences (THM) in Germany, this process is being further developed to achieve even better reproducibility. During the optimization process, special additively manufactured guide wheels were designed to enable the most laminar air flow possible over the concrete slab under investigation. This is accompanied by the best possible reproducible environmental conditions, which make the test feasible worldwide and thus establish comparability. Several test executions with different concrete mixes and fibers demonstrate the functionality of the test setup. Basalt fibers were also investigated for the first time in a direct comparison with polypropylene fibers.

The assessment and maintenance of reinforced concrete structures depends largely on knowledge of the chloride content and chloride ingress. Common methods are the wet chemical analysis of drill dust or powder from ground drill core segments. However, due to the homogenization process, this approach often fails to detect locally elevated chloride levels. A state-of-the-art alternative method is laser-induced breakdown spectroscopy (LIBS), which offers rapid analysis and the possibility of detecting several chemical elements simultaneously. This method is particularly characterized by its ability to measure light elements such as hydrogen, carbon or sodium. The spatial resolution of LIBS is usually 0.25 mm but can be increased to 0.1 mm or less if required. BARG, is the first commercial building materials laboratory in Germany to use LIBS in practice. The current LIBS setup enables rapid, spatial quantification of the chlorine content and at the same time the creation of element maps that visually represent the distribution of essential elements in the concrete. This method can be used to localize areas of elevated chlorine content, particularly in cracks or near reinforcing bars. With the ability to analyze several elements simultaneously, LIBS can determine measurement points associated with the cement phase and, taking into account the water content, relate the measured contents directly to the cement mass. The detailed ingress profiles determined by LIBS provide essential data for the estimation of accurate chlorine diffusion coefficients, which are crucial for probabilistic lifetime predictions. The estimation of the carbon distribution enables the localization of carbonated regions and their effect on the chloride distribution. The possibility of quantitatively determining the sulfur distribution also indicates areas that are affected by a possible sulfate attack. The presentation uses practical examples to demonstrate the possibilities and advantages of the LIBS method. In addition, the newly published leaflet B14 of the German Society for Non-Destructive Testing (DGZfP) will be presented, which describes the use of LIBS for the quantitative determination of chloride content in concrete.

In order to avoid corrosion critical situations, preventive measures can be taken for particularly susceptible parts of the structure. The project-specific selection of corrosion protection measures for reinforcing steel should be based on the overall concept of sustainable construction, taking into account technical and economic aspects as well as the preservation of the ecosystem and the environment. For construction with stainless reinforcing steel, this means using the product with the lowest content of alloying elements on a project-specific basis (assuming equivalent sustainability of the production process of the considering products), while still meeting the technical requirements. On the technical side, the required level of corrosion resistance of the stainless reinforcing steel has to be determined on a project-specific basis. The laboratory test method ECISS provides a tool for determining the actual corrosion resistance of stainless reinforcing steels, taking into account the type and content of alloying elements, as well as any process-related improvement of the reinforcing steel. This article presents test results using this test method.

Calcium aluminate-based materials have shown high resistance to the chemical and biological attack in sewer systems and thus are used to protect Portland cement-based structures and increase their durability. In this direction, a protective calcium aluminate-based coating, designed to be sprayed in a thin layer onto newly built wastewater infrastructures, was developed by Imerys Aluminates. The question arises of the ability of the coating to maintain its protective function when a crack is initiated in the concrete support and possibly propagates into the coating. Several phenomena may develop and condition the behavior of the cracked aluminous coating, including the self-healing of the cementitious material and the penetration of micro-organisms to reach the substrate. To study this coupling of cracking and biodeterioration in the lab, a method for the generation of representative cracks was developed. The three-point bending test was performed on these coated mortars to initiate cracks with a specific opening width, to be maintained after unloading. Then, to understand the mechanisms of biodeterioration, cracked and uncracked specimens were exposed to the BAC test which reproduces biodeterioration conditions observed in sewer environments. The biodeterioration process was monitored in terms of analyses of the composition of the leached solutions to quantify the calcium and aluminum leaching. The superior resistance of the coated substrates was significantly proven. The presence of a crack in the coated substrates has no influence on the leaching species for the specific duration of the test.

To determine the resistance of a concrete against chloride penetration, the so-called Rapid Chloride Migration (RCM) Test is often used in Europe, for which different test specifications with different boundary conditions exist. In addition, alternative methods are being considered: firstly, a Modified Chloride Migration (MCM) test, in which the charge flow through the test specimen is utilised, and secondly, the use of the electrolytic resistivity of the concrete. In both cases, the migration coefficient is determined via a regression function. Compared to the current standard RCM test, the charge measurement method and the use of the electrolytic resistivity offers the advantage of a significantly shorter test duration and less testing effort. However, the available data on the correlation between the individual methods still needs to be further developed, particularly with regard to different boundary conditions in the RCM test due to different test specifications. In the investigations presented here, conventional RCM tests with different compositions of the catholyte solution were used for concretes and mortars and additional measurements were added to determine the charge flow and the electrolytic resistivity. The results so far indicate that existing correlations between the individual test methods must be formulated depending on certain test boundary conditions.

Oxidation of sulfide-bearing aggregates is a major cause of concrete damage in numerous buildings in Trois-Rivières, Canada; Connecticut, USA; and Donegal County, Ireland. In the presence of moisture and oxygen, pyrrhotite oxidizes to form iron- and sulfate-rich secondary minerals that cause internal sulfate attack. This study evaluates the deleterious potential of a pyrrhotite-bearing aggregate for use in concrete using the oxygen consumption test. This test quantitatively assesses sulfide oxidation potential by measuring the oxygen consumed by oxidation in a sealed cell containing a layer of the ground aggregate material in the presence of a specified moisture content. A series of aggregate samples, carefully controlled for total sulfur content ranging from 0.03 to 0.82 wt%, are used to evaluate the response to the oxygen consumption test. Polished concrete slabs were prepared from the base aggregates for semi-quantitative chemical in-situ analysis by µXRF to determine the proportions of the various sulfide minerals. The oxygen consumption ranged from 4 (control) to 24% for the richest sample containing 0.82% total sulfur. A strong correlation factor (R2) of 0.95 was obtained between the amount of oxygen consumed as a function of the volume content of iron sulfides, thus potentially reflecting the effect of reactive iron sulfide content on concrete deterioration. Analysis of a larger number of samples is needed to establish a limit on the amount of oxygen consumed for the quality control of sulfide-bearing aggregates.

The durability of concrete is often compromised by water and ion ingress. Water ingress through capillary suction is one of the mechanisms by which water and ions enter concrete. The porosity of 3D printed concrete is concentrated at the interlayer; therefore, the overall water absorption is increased at the interlayer. Several chemicals exist that reduce the water absorption of concrete. These chemicals are normally either applied to the casted concrete after curing or added integrally to the fresh concrete during mixing. Silicones are a chemical family that can be used either in post application or integrally, to reduce water absorption. While these silicones reduce water absorption, the pores remain open to water vapour and other gasses. Experiments were conducted to determine if silicones can reduce water absorption. Silicones were applied on top of each layer during the printing process. Silicones were also post applied to the side surface of hardened printed samples. The results show that both methods are suitable to reduce water absorption with the application between the layers lowering the overall absorption the most. However, the application between the layers did reduce the interlayer bond strength of the 3D printed concrete.

This paper presents a comprehensive literature review on the long-term effectiveness of electrochemical realkalization (ER) in repairing chloride-induced corrosion in reinforced concrete structures. Chloride-induced corrosion is a significant challenge in reinforced concrete, leading to structural degradation and substantial economic and environmental impacts. Traditional repair methods, such as patch repairs, cathodic protection, and concrete overlays, often fail to address the underlying chloride contamination, resulting in recurring corrosion issues. ER has emerged as a promising alternative by restoring the alkaline environment necessary to protect steel reinforcement and halt corrosion progression. This review explores the principles of ER and its application process and compares its effectiveness with traditional repair methods. Additionally, it analyzes long-term studies, highlighting factors such as material properties and environmental conditions that influence the success of ER. The findings underscore ER's potential as a cost-effective and durable solution for extending the service life of chloride-contaminated structures, particularly in challenging environments.

Service reservoirs are an integral part of the potable water distribution network and concrete is the preferred material of choice. Deterioration of concrete in service reservoirs is a lesser-known problem. The symptoms are surface deposition of minerals requiring constant cleaning between operations. Debonding and dislodging of aggregates affecting the operation, gradual reduction of the cross-section of the concrete wall and rebar corrosion in reinforced segments. Calcium compounds that dominate the hydrated cement and thus concrete microstructure will be leached away to the potable water which is low in calcium. Data from over 20 reservoir investigations confirm leaching as the dominant mechanism. The damage was evident in petrographic investigations, from which a depth of leaching was determined. Rate of leaching was defined as depth of leaching/years of service. The rate of leaching and NDT score (a unitless entity) shows no relationship when data from all structures are brought together. The lack of relationship is due to many reasons including differences in initial permeability of concrete, quality of water (pH), rate of flow of water and variable maintenance programmes. For example, half of the structures reported leaching depth > 10 mm, for a life span of 30–90 years. Equally, structures that have been in service for 60–70 years, recorded a leaching depth below 10 mm. The NDT data presented in the form of augmented reality and also the rate of leaching allows asset managers to take informed decisions for managing the assets. Future work should focus on quantifying the water quality among other key parameters.

Shrinkage in concrete structures can lead to cracking and increased deflections among other effects. In South Africa, drying shrinkage potential of concrete under ordinary environmental exposure condition is tested according to the methods outlined in codes such as SANS 6085:2006b, ASTM C 157M-08, BS EN 12390-16:2019 and AS 1012.13-1992. The SABS Method 1085:2021 is also used when testing for accelerated shrinkage. Using test results from the two approaches above, the aim of the study is to enable practitioners interpret results and be able to choose appropriate test methods from the same. Three concrete mixes with water/binder ratios of 0.45, 0.55 and 0.65 were cast in the laboratory. One set of samples was cured for 3 days, while the other was cured for 10 days before testing commenced. The mixes were tested for shrinkage according to SANS 6085:2006b and SABS Method 1085:2021. From test results, cumulative shrinkage strains increase with time while the rate of shrinkage is higher at early ages. A higher temperature increases the rate of early age shrinkage, although it reduces ultimate shrinkage. On average, shrinkage reduced by 40% when the SABS Method 1085:2021 was used. While the study adds to the database of shrinkage measurements, more robust and analytical studies are necessary to predict the shrinkage potential of concrete accurately and quickly.

Cement is one of the concrete materials associated with the highest environmental concerns. Its production is energy-intensive and releases a significant amount of CO2, contributing to climate change and environmental degradation. The concrete industry actively seeks sustainable alternatives to traditional Portland cement to address these challenges. The expectation is to develop low-carbon cement with waste materials as part of the cement constituents. Using ceramic waste powder (CWP) as a partial replacement for cement is a promising approach to achieving sustainable concrete. This addresses both environmental concerns and resource conservation. Incorporating CWP into cement constituents also possesses the potential to improve concrete microstructure, mechanical, structural, and durability properties. This paper reviews the microstructure and durability properties of concrete mixtures containing CWP as partial cement replacement. Ceramic waste powder originates from different products such as tableware, cookware, pottery, electric insulators, tiles, and sanitary wares. This study focuses on concrete made of cement containing ceramic waste tiles and sanitary waste powder. The results highlight CWP’s promising ability as an alternative cement material. However, the available literature lacks enough evidence to conclusively classify its role as an inert filler or supplementary cementitious material, mainly due to uncertainty surrounding its pozzolanic reactivity.

Waste tyres derived from automobiles are difficult to recycle due to a complex polymeric matrix and additives used in tyre manufacturing. This has resulted in more waste tyres being disposed in landfills or incinerated, while granulated waste tyre rubber (WTR) could have been used in construction as a replacement material for mineral aggregates in concrete. This study aimed to produce structural concrete (with a minimum characteristic strength of 25 MPa at 28 days) using 13 mm WTR as a partial replacement for the coarse mineral aggregate at replacement intervals of 5, 10, 20 and 30% by volume, while maintaining a constant water-to-binder (w/b) ratio of 0.40. Results indicate a significant reduction in the mechanical strength and durability (oxygen permeability and water sorptivity) index of concrete with increased WTR replacements. Portland cement (PC) was partially replaced with 15% condensed silica fume (CSF) by mass to enhance the strength and durability performance of concrete. Results showed that the strength of concrete made using PC decreased by 63.8% from 67.1 to 24.3 MPa when comparing the control mix and concrete at 30% WTR replacement. Furthermore, at 30% WTR replacement for concrete made using PC, the oxygen permeability index decreased by 13.5% from 10.19 for the control mix to 8.81, which indicates poor durability performance, while the water sorptivity index increased significantly at 20 and 30% WTR replacements compared to the control mix with the water sorptivity index of 9.35 mm/h0.5. It was also observed that concrete mixes made using CSF had a higher strength and improved durability compared to those containing PC alone. The results from this study indicate that WTR could be used in concrete for structural applications, while reducing the demand for mineral aggregates mined and waste tyres incinerated or disposed in landfills.

This research aims to develop sustainable waste management practices in the construction industry by substituting components in 3D printing concrete (3DPC) with recycled glass waste material. This substitution not only improved concrete durability but also reduces environmental demand and promotes sustainability in the construction industry. Waste recycled glass was incorporated as cementitious material and fillers to formulate an environmentally friendly 3DPC. The study considered four aspects: waste material characterisation, mix design formulation, formulation modification optimisation for 3D printing, and potential of the obtained paste in a circular economy. Characterisation of materials was performed using X-ray fluorescence (XRF) to determine the elemental composition, X-ray diffraction (XRD) to determine the phase analysis, Fourier Transform Infrared Spectroscopy (FT-IR) to determine the structural bonding, and Particle Size Analysis to determine the particle size distribution. The findings provide a comprehensive understanding of the effects of incorporating waste glass as filler in formulations suited for 3DPC. It contributes to knowledge regarding the optimal percentages and replacement levels of these waste materials to achieve the desired 3D printing properties. Ultimately, this research aims to enhance the sustainability of buildings and infrastructure by addressing material selection, energy efficiency, local sourcing, design optimization, recycling and reuse, durability, labour reduction, and waste reduction.

The development and testing of low-carbon alternative masonry units (AMUs) in mitigating the carbon footprint of traditional burnt clay and cement-based masonry units is germane to achieving sustainability. This study explores one-part geopolymer material technology used in the development of eco-friendly AMUs. Fly ash-blast furnace slag and fly ash-metakaolin-based one-part geopolymer concrete masonry units, activated by solid sodium hydroxide, powdered calcium hydroxide and solid sodium metasilicate pentahydrate geopolymer mixes were developed and tested for strength and durability. The compressive strength and water absorption of the AMUs were characterised at 7- and 28-day under ambient curing conditions. Additionally, the extent of efflorescence was monitored and reported. The results show suitable 28-day compressive strengths of 18.4 MPa and 6.1 MPa for fly ash-blast furnace slag and fly ash-metkaolin-based units, respectively, surpassing 4 MPa and meeting the prescribed minimum requirements for single-story masonry structures. The water absorption characteristics in both cold and boiled conditions remained below the 10% limit for concrete masonry units and the initial rate of absorption (IRA) was acceptable. Additionally, the extent of efflorescence was minimal to non-existent.

Limestone calcined clay cement (LC3) is one of the most promising technological breakthroughs for high-performance ternary blended cement. This is due to its significantly lower quantities of clinker and lower carbon emissions compared to conventional concrete with great potential to be adopted as a cement alternative globally. Recycled fine aggregate (RFA) is often considered the least preferred option for concrete recycling, with numerous sources highlighting their adverse impact on critical concrete properties, including compressive and tensile strength, modulus of elasticity, water absorption, shrinkage, carbonation, and chloride penetration. In this study, five mixes were made: the control (without limestone calcined clay), the LC3 mix, and the LC3 mix with 25%, 50%, and 100% recycled fine aggregate as a replacement for natural sand. Concrete specimens were prepared at a water-to-binder ratio of 0.55, and tests were performed to investigate the effect of RFA on the compressive strength and water absorption of LC3 concrete. The findings indicate that the total replacement of natural sand with unwashed RFA increases the compressive strength and reduces the water absorption of LC3 concrete by 9% and 14%, respectively.

This research investigates the utilization of secondary gold mine tailings (SGT) in concrete production to address waste management concerns. This approach offers an environmentally friendly substitute for conventional sand, exploring various SGT proportions (ranging from 0% to 100%) as replacements for fine aggregate in concrete. The investigation assessed the fresh, mechanical, and durability properties of concrete made with SGT. The incorporation of SGT diminishes concrete workability while replacement levels of up to 75% exhibit higher fresh concrete density than reference concrete. The findings show that replacing up to 25% enhanced compressive strength, while up to 50% replacement improved splitting tensile strength compared to the reference concrete. Nevertheless, all concrete specimens achieved satisfactory strengths. Furthermore, the durability findings show the concrete specimens were less vulnerable to oxygen, water, and chloride attacks, signifying good-quality concrete. The study proposes substituting SGT for crusher sand to address environmental concerns, lower production costs, and conserve natural resources.

The recent industrialization and urbanization have placed heavy demand on the usage of concrete as construction materials. Therefore, large quantities of raw materials and natural resources are required to meet the large concrete production worldwide. Concrete is made up of cement, sand, stone, and admixtures to alter its properties when necessary. Concrete constituents are finite materials that can be easily depleted due to the increasing demand for concrete. A considerable amount of waste glass (WG) that usually constitutes a nuisance to the environment is now processed as fine aggregate and cement replacement used in concrete. This is an attempt to reduce cost, improve properties and reduce the total embodied carbon in concrete manufacturing of approximately 8% of the world's CO2 emissions. Studies have shown that WG constitutes a large amount of silicon oxide and relative proportions of calcium and aluminium oxides. This shows that WG can be regarded as pozzolan when it is finely grounded into powder. It is important to examine the concrete microstructure and durability properties to ascertain the effectiveness of WG powder as a cement replacement material in concrete. This paper reviews the microstructure and durability properties of concrete that contains WG powder. It summarises existing knowledge of the successful use of WG powder in concrete.

The rising demand for housing, propelled by population growth, calls for affordable and reliable construction materials. Compressed Stabilized Earth Blocks (CSEB), an environmentally friendly construction material, serves as a potential solution. The clay soil retrieved from the Olifantsfontein Resource Facility, previously unused and occupying valuable space, was repurposed to produce CSEB, aligning with the company’s waste reduction commitment. Soil analysis following South African National Standards (SANS) and American Society for Testing and Materials (ASTM) guidelines, revealing poorly graded sand with silt and clay. River sand was chosen based on particle packing theory to achieve a well-graded PSD. Three mixtures with varying clay and river sand proportions, while maintaining a constant cement content of 5%, were prepared. Optimum moisture content was determined through trials with different moisture levels. A compressive strength test, both dry and wet, along with a water absorption test, were conducted to evaluate the brick’s performance under variable conditions. Results showed that increasing clay content improved compressive strength, classifying the bricks as load-bearing. The study’s compressive strength test results ranged between 3–5 MPa, with dry compressive strength outperforming wet compressive strength. On average, the three mixtures exhibited a water absorption of 11.31%, although mix designs with varying clay content showed different average water contents due to the water-absorption properties of cement and the water-holding capacity of clay. Overall, the findings demonstrate the potential of Olifantsfontein clay as a sustainable construction material for meeting the increasing demand for housing.

The use of waste glass as fine aggregate in concrete offers a sustainable solution for reducing the environmental burden associated with glass disposal. However, incorporating waste glass as fine aggregate poses risks of expansion and strength reduction caused by alkali-silica reaction and the weak glass-paste interface. To address these challenges, the addition of mineral additives has shown promise in improving durability and offsetting strength reduction. Therefore, this paper presents findings on the sustainable use of waste glass in Portland cement concrete containing metakaolin. The waste glass replaced 10–40% of the fine aggregate, while metakaolin replaced 25% of the Portland cement. The addition of metakaolin in waste-glass-aggregate concrete significantly enhanced both strength and durability. All mixes containing waste glass and metakaolin exhibited higher 28-day compressive strength and better durability performance compared to the control. Among these, the 20% waste glass replacement achieved the highest compressive strength while the mixture containing 40% waste glass displayed outstanding resistance against oxygen permeation, water absorption, and chloride conduction. These findings demonstrate that waste glass can replace up to 40% of fine aggregate without compromising strength and durability when combined with metakaolin. This approach not only offers a sustainable means for concrete production but also addresses the environmental concerns associated with waste glass disposal.

An attempt is made in this research work to find out if the foam concrete can be used for industrial roof. Sodium Lauryl Ether Sulphate (SLES) liquid as foaming agent and fine M sand passing through 1.18 mm sieve is used in the present study. Basic mechanical tests were conducted on different densities and cement to sand mix ratios of foam concrete. The obtained results were compared with the test results of the normal mix without foam. From the test results, it was found that the foam concrete of density 1500 kg/m3 and higher with a cement to sand mix ratio of 1:1 can be considered to be used in places where normal cement mortar of cement to sand mix of 1:2 and higher are being used for structural purposes. Two types of foam concrete slabs with different reinforcements and 50 mm thick was subjected to flexural test and checked if it can be used for industrial roof from flexural strength point of view. Both types of foam concrete slab specimens cast satisfied the minimum strength required for the industrial roof subjected to bending both from strength and serviceability point of view. Foam concrete slab of density 1500 kg/m3 with a cement to sand mix ratio of 1:1 of thickness 50 mm with one layer of mild steel welded mesh and 2 layers of hexagonal or rectangular galvanized iron woven mesh can be used as precast industrial roofing element for a span of about 1.7 m.

A concrete mixture that has been used successfully for some time, can suddenly exhibit unpredictable and undesirable effects due to changes in the cement composition during production or due to a change in the cement manufacturer or supplier for a construction project. The change in the composition of cement, along with the addition of admixtures (specifically superplasticizers) leaves concrete mixes vulnerable to inconsistent behaviour and possibly incompatibilities. This study aims to identify the components that leave a mix prone to inconsistent behaviour and the consequences thereof in practice. It was found that the C3A and alkali content in clinkers are of high importance when faced with inconsistent behaviour. These components influence a mix’s compatibility with sulphates and superplasticisers, as well as its slump flow and set times characteristics.

This study investigated the effect of replacing natural dune sand with fine recycled concrete aggregates (fRCA) produced using real concrete construction and demolition waste (CDW) and with a maximum particle size of 1.18 mm on the fresh and hardened properties of concrete. Concrete with w/b ratios of 0.45 and 0.60 was produced. Natural fine aggregates comprised of a 50/50 mix of dune sand and crusher dust. fRCA replaced the dune sand portion of the natural fine aggregates by 0%, 30%, and 50% of total natural fine aggregates by mass. Results showed that workability of fresh concrete was reduced as fRCA replacement level increased while hardened properties of concrete, including compressive strength, gas permeability, sorptivity, and water-penetrable porosity, were comparable at all replacement levels for each w/b.

It is projected that Africa’s population will increase from 1 billion to more than 2.4 billion people by 2050. Thus, the projected population growth and rapid urbanization will place tremendous pressure on Africa’s existing urban infrastructure and escalate the demand for new infrastructure developments. The escalation for new infrastructure development will only further enlarge the carbon footprint of the African cement and concrete industry. Solutions like graphene provide the opportunity for a reduced carbon footprint as well as economic stimulation through a global emerging market. This study aims to develop an overarching strategy to establish an Afrocentric graphene ecosystem in the South African cement and concrete industry. This was done by conducting a SWOT analysis of graphene which was then used to lay out a roadmap to be followed to achieve the mentioned aim. The findings of the SWOT analysis indicated that although graphene provides drastic improvements to the material properties of cement-based materials, it is currently not financially viable since graphene needs to be imported. However, the South African cement and concrete industry is identified as the access point to implement graphene at a large scale due to the large quantity of cement and concrete consumed by the South African build environment. Thus, the cement and concrete industry is seen as the catalyst to drive down the cost of graphene. In addition, South Africa is twenty years behind developed economies and lacks the sophisticated infrastructure to manufacture and implement graphene along with industry specialists to service the market. Thus, by focusing on four critical short-term focal points namely manufacturing, understanding, implementing and marketing, South Africa has the opportunity to develop an Afrocentric graphene eco-system. However, this would require South Africa to move swiftly and intently to seize the opportunity graphene presents.

In September 2018 a Canadian Company initiated litigation claiming UK inventors infringed a patent describing an invention the inventors had made in 2003. It had subsequently purchased this patent from the inventors former UK employer. Then, in February 2019, after receiving the inventors defence and cross-claim, the Canadian company filed an entitlement claim to a 2005 invention by the same inventors. The two cases were litigated in Australia. The relevant inventions related to the corrosion protection of steel in reinforced concrete. This work considers features inventors need to address in the context of litigation arising from their inventions. Examples are provided to illustrate the need, from the perspective of an inventor, to understand the allegations and study the event timeline to avoid the negative effects of the use of hindsight.