This chapter delves into the necessity for a new development paradigm in polymer-concrete composites, commemorating the 100-year anniversary of the first patent on polymers in concrete. It traces the evolution of the general material concept into various types of concrete, including Polymer Concrete, Polymer Modified Concrete, Polymer Cement Concrete, and Polymer-Impregnated Concrete. The chapter also explores the fascination surrounding the substantial impact of small amounts of polymer on concrete properties, detailing the different types of polymers used and their percentages in concrete. Additionally, it discusses the scope of concrete-polymer composites and their applications, such as polymer overlays, coatings, repair mortars, and crack repair, emphasizing the potential for innovation in this field.
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Abstract
In less than a century, concrete has become the most commonly used construction material worldwide. Today, it is difficult to imagine concrete entirely devoid of polymers. The implantation of polymers into concrete has taken effect in the form of Concrete Polymer Composite [C-PC = PMC + PCC + PIC + PC]. Several milestones are recognised in the development of C-PC. They are discussed here with particular emphasis on the innovative milestones that shaped the use of polymers in concrete. As the difference between polymer cement concrete and ordinary concrete diminishes, the question: “What should the paradigm of C-PC development be?” arises.
1 Introduction: Need for a New Paradigm
It is symbolic that our considerations take place one hundred years after the first patent (L. Cresson, 1923) on polymers in concrete was received [1]. Simultaneously, more than fifty years ago, the concept of “polymer in concrete” began to be thoroughly developed [2, 3]. Gradually, the general material concept (Fig. 1) has been transformed into various kinds of concrete – Polymer Composites C-PC = MPC + PCC + PIC + PC, see Table 1. There is fascination surrounding the fact that such a small amount of polymer can have such a great effect on concrete properties, see Table 2.
Fiber-reinforced polymers for strengthening Concrete, FRP-C
Polymer repair mortars
Polymer crack repair
Table 2.
Content Polymer in Concrete, P/Con. %
Type of Polymers
P/Con. %
Nano PCC
<0.10
PMC
<0.15
PCC pre-mix
1–3
PCC post-mix
1–3
PIC
3–8
PC
8–12
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Polymers in concrete serve in a multitude of ways as significant modifiers in the processing (“binders”) of concrete. Functional polymers are used due to their particular native properties and synergy, created by their own: bonding, adhesion, chemical reactivity, viscosity, regulation, lubrication, hydrophyllic/hydrophobic, water repellent, thermo-setting, thermo-plasting, chemo-setting and so on.
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The results of the main research gradually revealed a mechanism of polymer in concrete modification (Fig. 2). The basis has been the utilisation of the synergy of polymers in concrete because their influence on the properties of the product is much higher than that declared from its mass share.
Fig. 2.
Mechanism of polymer in concrete modification
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The sixteen International Congresses since 1975 have marked the milestones in the C-PC development. The rapid development of the discipline and collection of new knowledge followed the incubation period. At a certain point, publications started to bring in less new knowledge (involving mainly confirmations or revisions). The literature also expressed doubts and negations, secondary discoveries or even repetitions. The maturity period was followed by “fatigue with the topic”. The end of the cycle marked the beginning of new hysteresis (Fig. 3a), typically with a new paradigm, which is initiated on a much higher level of knowledge [6].
“Delusion of hysteresis” intrinsically includes a negative arrow of time and is not possible in physics categories. The “time trap” can be bypassed by introducing the discontinuity between the displaced logistic curves (Fig. 3b). The sense of hysteresis remains and corresponds to the researcher’s state of mind in the reference period. The authors feel that this point is being addressed in terms of Concrete-Polymer Composites. In the field of C-PC, we have experienced the entire scientific cycle. This statement is the consequence of our question, which we asked on the 16th ICPIC: “Is polymer still the factor that contributes to progress in concrete technology?” [5].
The same Congress, however, retains and confirms the Congresses’ motto “polymers for resilient and sustainable concrete infrastructure” [7]. The Concrete-Polymer Composites research area needs a new paradigm of development. Certainly, this is an arbitrary statement. Usually, that is a conclusion ex-post – it just happened. As authors, we would like to emphasise strongly that the basis of our statement is not pessimism; on the contrary, we would like to declare our deep confidence in the C-PC development. What is more, we are not alone in this belief. In 2022, a systematic review on C-PC was published [8] by three scholars from Melbourne University. Furthermore, the topic, similar to the ICPIC 2018 topic, was oriented towards “durable and resilient infrastructure” (!). In this paper, it is duly noted that the annual number of papers on C-PC is increasing (Fig. 4). According to the conclusions of the authors [8], the following particularly promising directions can be mentioned: corrosion inhibitors, electrical insulators, energy absorbers (vibration-damping), waterproofing, durable and resilient (high durability and ductile) means for infrastructure. Those “promises” are already pre-established applications. The future is always more unpredictable than it seems, which does not distract from the importance and need of forecasting.
Fig. 3.
Development of the state of knowledge according to the: a) apparent hysteresis; b) displaced logistic curves [6]
Fig. 4.
The growth trajectory of publications with topics on polymer-modified cementitious composites over the past 40 years (1982–2022) [Data source: SCOPUS – Search dated: 1 June 2022] [8].
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2 From Application of Polymers in a Mineral Matrix to Understanding Interactions Between Organic and Mineral Phases
The combination of polymers with cement concrete dates back to the beginning of the twentieth century because the origin of cement concrete itself only dates back to the second half of the nineteenth century. Natural polymers, however, were already used in ancient times to enhance the properties and durability of plasters, mortars and concretes [9]. Today, analysis of the composition of ancient binders and mortars with proven durability reveals the hardening activation methods, and these methods serve as guidance to improve the hydration mechanisms of pozzolans and industrial by-products to develop more sustainable binders for the construction industry [10].
Although it was soon recognised that the combination of hydraulic cement and polymer in concrete creates opportunities for beneficial synergies that result from the intended interactions between cement and polymer particles in the fresh mix, between cement hydration and polymer hardening systems during curing, and from the interactions between hardened cement hydrates and hardened polymer structures, it took several decades and successive modelling steps to understand and master the microstructure formation in C-PC [11].
Several milestones can be observed on the road to building the PCC microstructure formation model, which run parallel with the history of the ICPIC Congresses, see Table 3 and [12].
Table 3.
Milestones in the development of C-PC, marked by International Congresses on Polymers in Concrete, ICPIC [6]
Congress No
Year
Main theme
I
1975
Innovation – progress in concrete technology: PIC, PCC, PC
II
1978
Applications – trials and errors
III
1981
Usability testing
IV
1984
Material model
V
1987
Control of properties
VI
1990
Effectiveness of polymer utilisation
VII
1992
Evaluation, simulation, optimisation
VIII
1995
Modelling: durability and synergy
IX
1998
Micro–macro-structure relations (nanotechnology, application of plastic recycles)
X
2001
Sustainable C-PC
XI
2004
Integrated PCC model; synergy. Water-soluble polymers as modifiers
XII
2007
Sustainability; nanotechnology as the driving force
XIII
2010
C-PC of high usability
XIV
2013
Modelling the processes of binding and curing. Synergy between the components. Pursuing new development directions
XV
2015
Great expectations. Potentially “mature” C-PC
XVI
2018
Does polymer still create progress in concrete technology?
At the first ICPIC Congress in 1975, H.R. Sasse [13] already presented the interaction between polymer admixtures and cement hydrates. He assumed that the polymers formed extremely thin resin films or net-like structures on the hydrate surfaces. During hydration, these films are penetrated and swallowed up by newly formed hydration products, thus losing their effectiveness. That assumption, however, is only valid for the low-ratio polymer admixtures in his study. At first, the models only envisaged the interaction of polymer, cement paste and aggregates in the hardened state [14, 15]. The original three-step model proposed by Y. Ohama [16] took into account the hardening process of the polymer phase. Subsequently, numerous specifications and modifications to this model have been presented [12]. Beeldens et al. [17] proposed an integrated model, in which the interaction between cement hydration and polymer hardening is integrated. Dimmig-Osburg [18] included the adsorption of polymer on cement particles, whereas Ye [19] considered possible flocculation effects of the polymer particles, leading to discontinuous distribution of polymer throughout the microstructure. Enhancement of SEM resolution and magnification capabilities also enabled to study [20] the effect of very low amounts of polymer on the microstructure at the nano-scale, e.g. to study the positioning and influence of water-soluble polymer in between hexagonal Portlandite plates [21]. The difference between micro- (Fig. 5a) and nano-interaction (Fig. 5b) is clearly represented in Fig. 5. It is obvious that the above-presented Polymer Cement Concrete technology developments and microstructure models only and solely involve physical mechanisms and physical interactions by which the synergy phenomena are obtained. Compared to physical interaction, chemical interaction is not considered in many cases.
Fig. 5.
(a) Polymer bridging between crack-edges of concrete on micro-level [49]; (b) Polymer bridging between Portlandite plates on nano-level [11]
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3 Lessons from the Past
In searching for new developments, looking at the past is frequently a sparkling source of inspiration. As a sector, the construction industry accounts for more than 10% of global GDP (in developed countries, construction comprises 6–9% of GDP), and employs around 7% of the total employed workforce around the globe (accounting for over 273 million full- and part-time jobs in 2014). Construction is a major source of employment and a driving force of the economy in most countries [22].
The construction sector has an important impact on the environment: as much as 50% of all materials extracted from the earth’s crust are transformed into construction materials and products. In relation to the total energy consumed globally, energy used in the construction sector in the process of erecting and operating buildings accounts for 40% of this consumption. Moreover, these same materials when they enter the waste stream, account for some 35% of all waste generated prior to recovery [23]. Greenhouse gas emissions from material extraction, manufacturing of construction products, as well as the construction and renovation of buildings are estimated at 5–12% of the total national GHG emissions. Greater material efficiency could save up to 75% of these emissions by 2060, compared to the 2017 level [24]. These numbers put the construction industry “in the picture” for sustainability efforts and sustainable consumption and production action plans.
Cement production is a major energy and primary materials consumer, as well as a major greenhouse gas emitter. Therefore, if we only consider cement consumption as an indicator for the contribution of construction to ecological improvement, the numbers are not flattering (Fig. 6). Worldwide consumption of cement is still increasing, only the economic recession kept the level of worldwide consumption of cement nearly constant between 2013 and 2018 but, since then, consumption is steadily increasing again.
Fig. 6.
Estimated evolution of cement and clinker consumption in sustainable cement industry. Data source [25]
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Material resource efficiency can be applied across a construction project’s life cycle, with the greatest benefits at the early stages, where more opportunities arise to design out waste and investigate material choices. Greater material resource efficiency requires the various parts of the construction supply chain to work together for a common goal, as a decision by one part could adversely affect another. There is an increasing awareness that improved material resource efficiency would produce benefits across the industry, such as cost savings, reduced environmental impact, and an enhanced reputation. Exploiting the synergies between construction materials in composites, e.g. C-PC, is a way towards efficiency enhancement. In all of the above development areas, the combination of mineral and organic binders is still a virgin research field where the same benefits as in C-PC will be possible.
4 Searching for Novelties
4.1 Assumptions of the Search
The question arises: “where should we seek novelty?” The most promising areas of research for the future are:
new material solutions;
new technological methods;
new applications;
novelties in unexpected areas.
It should be assumed that this novelty will be found in the frame of sustainability requirements; sustainability remains the cogent commandment [26, 27]. It also seems significant that, in general terms, the circular economy will define new paths of development and new challenges [28, 29]. The present state of knowledge can already bring some suggestions. According to the above categorisation, it could be:
the mineral-organic reaction as the gateway to the new generation of C-PC;
nano-modification as the new thrust in C-PC technology;
PCC as waste polymer product storage – paradoxically a new application area;
“novelties in unexpected areas” means, by definition, a collection of innovations of which we are not yet aware.
4.2 The Mineral-Organic Interaction in C-PC Properties Control
The physical and chemical interactions between polymers and Portland cement components and mineral filler define the technical properties of concrete. In comparison to physical interactions, there are more controversies and even lack of knowledge in regard to chemical interactions. Some of the reactions explain the failure mode of the materials, such as the hydrolysis of ester groups. Others explain the strengthening mechanisms, such as the formation of chelates.
Chemical bonding (ionic, covalent or metallic bonds), as an aspect of bonding of polymer materials to concrete at the molecular scale, has already been considered by Sasse and Fiebrich in 1983 [30], but they attributed bonding primarily to van der Waals forces (internal dipoles originating from dispersion, induction, orientation effects) and to micromechanical interlocking mechanisms. Recent studies, however, show evidence of chemical interactions between polymers and hydrating Portland cement. Chemical interaction may result in the formation of complex structures, as well as in changes in the morphology, composition, and quantities of hydrated cement phases [31]. Further research on mastering and exploitation of chemical interactions between mineral and organic phases is needed.
Chemical and physical interactions between cement and polymers are two sides of the same coin. Only when the chemical interactions between polymers and cement are clearly understood one can better explain the micro- and macro-structure relationship in concrete-polymer composites, which in turn serves the purpose of developing higher-performance materials. A clear picture of the chemical interaction that takes place between cement and polymer will be a good supplement to theories on physical interactions. Today, we are just a step away from this potential becoming a reality. Looking at the problem from another perspective will help to understand the application performance of these polymers in cement-based material modification [32].
Further progress will be made with an organic-inorganic composite, in which some components are chemically bonded, parallel to the physical interactions. If the two phases, polymer and Portland cement paste, are additionally partially linked together through strong chemical covalent or iono-covalent bonds, this gives extra cohesion to the whole structure and enhances the technical properties.
Existing studies have demonstrated ample evidence of chemical interaction between polymers and cement components in concrete-polymer composites through various analytical methods, including IR spectroscopy, thermal analysis, NMR microscopy etc. Recently, Molecular Dynamics simulations have proven to be the most effective method to study the interactions between inorganic-organic composites at this stage [33].
At the nanoscale, the interaction between polymers and cement hydration products contains several aspects, i.e. chemical bonding, van der Waals forces, hydrogen bonding etc. Different polymers may have different types of interactions with cement hydration products:
changing the molecular structure of hydration products and forming interactions with the hydration products, including chemical bonding and intermolecular force;
polymers affect the hydration reaction of cement and the molecular structure of hydration products;
in some cases, polymers significantly retard early hydration reactions.
All those interactions between the polymer and cement-based materials affect the end properties of concrete. Understanding these interactions is important to elucidate the relationship between the microstructure and macroscopic properties of polymer-modified cement-based materials. There is need for a scientific tool, which reveals the impact of polymer on concrete in macro performance and which will be able to control concrete performance in a reliable way.
4.3 Nanomodified Polymers for Resilient C-PC Infrastructure
In the past three decades, nanomodified polymers were introduced as a new alternative to standard polymers. Nanomodified polymers are synthesised by dispersing nanoparticles into the polymer resin. Changes in the polymer characteristics included but were not limited to low viscosity, high adhesion with other materials (e.g. aggregate and hardened cement), high tensile strength, high or low modulus of elasticity, low creep compliance, high thermal and electrical conductivity, as well as improved durability. Examples of nanoparticles used to modify polymers included carbon nanotubes (CNTs), graphene nanoplatelets (GNPs), alumina nanoparticles (ANPs) and nano clay (NC) particles, to name but a few. The change in polymer characteristics with the addition of nanoparticles is attributed to a dual effect of the nanoparticles that can induce physical and chemical changes in the polymer matrix. The first effect is that the nanoparticles act as a reinforcing particle/fibre in the polymer matrix, creating a particulate or fibre composite. On the other hand, the submicron scale of the nanoparticles allows them to interfere with and alter the polymerisation reaction and produce a new polymer with the desired properties. Researchers showed that nanoparticle content of less than 1.0–2.0% by weight of the polymer resin is sufficient to alter the polymer characteristics. The relatively low concentration of the nanomaterials necessary to induce significant changes in the polymer matrix is attributed to the very large surface area of the nanomaterials. The ability of nanomaterials to alter the properties of a polymer is mainly dependent on the efficiency of the dispersion technique [34]. Numerous dispersion techniques, including ultrasonication, centrifuging and magnetic stirring, have been reported in the literature with different levels of success. The level of dispersion success is a function of polymer rheology, the nanoparticle geometry, and its contents. Researchers showed that adding surface functional groups might improve the dispersion and enable the nanoparticles to interfere with the polymerisation process further [35].
Researchers have shown the ability to produce polymer concretes using nanomodified polymers [36, 37]. Polymer concretes with attractive characteristics, such as improved impact strength, high ductility, fracture toughness, and superior electrical conductivity were reported [36, 38]. Researchers demonstrated that Styrene-Butadiene Rubber (SBR) polymer-modified concrete (PMC) incorporating functionalised CNTs has much improved failure strain (Fig. 7) by up to 400% [38].
Fig. 7.
Failure strain for SBR PMC incorporating functionalised CNTs at seven days of age [39]
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This improvement in PMC failure strain was attributed to the ability of CNTs to alter SBR polymerisation. Furthermore, scanning electron micrographs (SEM) of an SBR film and SBR PMC incorporating functionalised CNTs are shown in Fig. 8 (a) and (b) respectively. The SEM micrographs demonstrate that CNTs also act as microfibres bridging microcracks, thus improving PMC failure strain [39].
Fig. 8.
SEM micrographs showing the interwoven functionalised CNTs affecting the polymer matrix and bridging its microcracks [a] SBR film [b] SBR PMC [39]
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Furthermore, researchers also showed the ability of a mix of pristine and functionalised CNTs to improve the mechanical strength, ductility, and fracture characteristics of epoxy polymer concrete (PC) [40]. Stress-strain diagrams with Epoxy PC incorporating a mix of pristine and functionalised CNTs demonstrate an increase in the material failure strain by up to 74%, while maintaining an appreciable tensile strength of 10 MPa (Fig. 9).
Fig. 9.
Stress-strain curves of Epoxy PC incorporating a mix of pristine and functionalised CNTs compared with neat epoxy PC [39]
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Fracture toughness measurements of Epoxy PC incorporating CNTs showed an increase of about 100% in the non-linear fracture toughness represented by the total critical J-Integral [41]. The improvement of the ductility and fracture toughness of PC incorporating this mix of CNTs was attributed to the ability of the CNT mix to increase the tensile failure strain and the shear transfer between the epoxy matrix layers, as demonstrated by the schematic model (Fig. 10).
Fig. 10.
Schematic representation showing the effect of a mix of functionalised and pristine CNTs on the polymer matrix in Epoxy PMC. The mixed CNTs allowed improving the failure strain and shear transfer in the Epoxy PC
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Finally, it was recently also shown that non-functionalised CNTs can significantly improve the electrical conductivity of PC [38]. The improved electrical conductivity of PC incorporating CNTs is attributed to the ability of the CNTs to percolate the polymer matrix with a CNT content close to 2.0%. Similar observations were reported for glass fibre-reinforced polymer composites incorporating CNTs [42]. The nanomodified PC with improved electrical conductivity can be used as a smart material due to its self-sensing capability.
Such PC with superior ductility, improved fracture toughness, and self-sensing capability can be used as a structural material in resilient structures observing significant seismic activities.
4.4 PCC as Waste Polymer Product Storage
In general, in the categories we have stated ahead of the problem (see Sect. 4.1), ‘even barely acceptable concrete from waste components’, will be a necessity dictated by the civilization. If yes, the request claimed in this sub-chapter is justified. Shortly after the 2018 ICPIC, I (L.Cz) considered the question, “Will recycled plastics be a driving force in concrete technology?” [43]. This is a dramatic forecast, to link together concrete – the absolute premium construction material with which the works of our civilisation are created – with plastic waste, but it is a social responsibility, and accented recycling is a way of survival.
What is more, I have outlined that it should be a paradigm setting the direction for a new development cycle, but there are several particularities to this [6]:
the objective is not to develop better concrete owing to polymer introduction but concrete with non-deteriorated characteristics despite the use of plastic waste;
the modifier is not the original liquid polymer used as a binder or co-binder but solid plastic waste as partial filler;
the changes should be attributed not to the pursuit of concrete refining and its provision with specific functionalities, but to “taking the load off” from plastic landfills, which now contain 70 billion tonnes of plastic and are still growing, estimated to last for 450–600 years. During this period, they will contaminate water, destroying organisms living in natural water, and damage the environment and its appearance;
the action does not result from the fact that concrete needs more polymer but from the environment not being able to take on more plastic waste, that is a higher amount of used plastic products. In this context, the slogan “good concrete is sustainable concrete” gains new meaning.
A few numbers to estimate how serious the problem is, are:
plastic production is 300 million tons annually;
seven billion tons of plastics are already in the landfill.
Roughly speaking, it will be possible to replace around 8% of aggregate by mass with plastics. This means that plastics in the landfill will at least no longer increase in volume. More information can be found in the breakthrough monography (492 pages): F. Pacheco-Torgal et al. (eds.): Use of recycled plastics in eco-efficient concrete. Elsevier 2018 [43].
4.5 Novelties in Unexpected Areas – Selected Examples
“Novelties in unexpected areas” represent a collection, which is the result of a task-oriented study. Such innovations advocate going beyond what is currently possible, and this call captures the public imagination. In civil engineering, however, we should play it safe according to the basic requirements of construction works. This social responsibility does not hamper building innovation but, instead, makes it more sophisticated. Some examples are presented, which at a given moment of disclosure could be treated as unexpected. “Unexpected” means that they are the result of a research programme, but also that it is not easy to forecast them. Retrospectively considering the research work of a given scholar, an achievement is always the result of a chain of values: ideas – research – innovation – validation/verification – implementation. At some moment during this change, a discovery loses its “unexpected” value. Nevertheless, the selected examples originate mainly in the scientific activity of Y. Ohama and D. Van Gemert and may be able to serve as inspiration.
Hardener-free epoxy as modifier is a promising new concept [44, 45, 50]. Conventional epoxy-modified mortars and concretes have inferior applicability due to the two-component mixing of the epoxy resin and the hardener, the toxicity of some hardeners like polyamine or polyamide, and the obstruction of cement hydration by the polymer. Even without hardeners, however, epoxy resin can harden in the presence of the alkalis or hydroxide ions produced by the hydration of cement in the epoxy-modified mortars. Such new epoxy-hydraulic cement systems provide an increase in flexural strength and a marked improvement in carbonation or chloride ion penetration resistance.
In hardener-free epoxy-modified mortars with polymer-cement ratios of 20% or less, the hardening degree of the epoxy resin is 50% to 90%, and unhardened epoxy remains. It is considered that the unhardened epoxy resin may be sealed during the hardened epoxy resin phase in the epoxy-modified mortars. In that way, the epoxy resin phase forms self-capsuled epoxy resin droplets. The self-capsuled epoxy resin can be broken at the cracking of the epoxy-modified mortar under loading. The unhardened resin in the self-capsuled epoxy phase may fill microcracks, thus providing a self-healing capacity to the mortar. The hydroxide ions, set free at hydration, act as hardener elements for the epoxy resin. The mechanism is presented in Fig. 11 and Fig. 12.
Fig. 11.
Hardening mechanism of epoxy resin in hardener-free epoxy-cement system [50]
Fig. 12.
Cracks caused by mechanical loading liberate unhardened epoxy from capsules. Epoxy hardens in contact with cement hydrate [50]
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Nitrite-type hydrocalumite as corrosion inhibitor of reinforced steel. Nitrite-type hydrocalumite [3CaO.Al202.Ca(NO2)2.nH2O] is a corrosion-inhibiting admixture or anticorrosive admixture which can adsorb the chloride ions (Cl−) that cause corrosion in reinforcing bars, and it liberates the nitrite ions (NO2−) that inhibit the corrosion. This is expressed by the formula in Fig. 13. It provides excellent corrosion-inhibiting properties to the reinforcing bars in concrete.
Fig. 13.
Chloride ions adsorption mechanism of nitrite-type hydrocalumite
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Consequently, polymer-modified mortar with superior corrosion-inhibiting properties and durability is expected when combining the use of nitrite-type hydrocalumite and hardener-free epoxy-resin. It is used as an effective repair material for deteriorated reinforced concrete structures [7, 40].
Water-soluble polymer (WSP) as an effective nano modificatory. If we change the polymer position from a micro-area into a nano-area, it will be bridging not between the crack-edges but between the hexagonal plates of Portlandite. The situation and the result will change drastically. On a micro-level, we will use 10% of polymer and receive 10 MPa of tensile strength. On the nano-level, we will use only 1% of polymer (ten times less) and receive 15 MPa of tensile strength. On a conceptual level, however, changing the polymer position from a micro-area to a nano-area is easier said than done. Ideas create innovation, but how is this technologically implemented? This has been possible due to the breakthrough achievement of D. Van Gemert and E. Knapen [46, 47]. If we use water-soluble polymer, WSP, instead of liquid polymer, the WSP, due to the thermodynamic conditions, will be placed in the “nano-area”. Understanding the nature of polymer-modified materials and various practical reasons, as well as the logic of concrete technology, shows that the water-soluble polymers could be a very promising modification of concrete. Only very few (literally) publications [13] addressed the particular microstructure of water-soluble polymer cement mortars and a fair amount of those microstructure–technical properties have been published before D. Van Gemert and E. Knapen’s discovery. This research field should be developed further. Researchers are focused on self-cleaning, self-repairing, high-adhesive, active products, such as air pollution reduction and nano-porous insulation products [48]. Progress has also been made with nano-coating on concrete. This is still at the stage of expectations, however, with a very promising outlook.
5 Conclusions
According to the authors’ statement, there is need for a new paradigm of C-PC development; it seems to be both the proper time and the proper reasons. A new paradigm should be found within the framework of sustainable development. The circular economy will define the paths of development and new challenges. The following have been considered as novelties:
new material solutions;
new technological methods;
new applications.
It turns out that it is difficult to formulate one “development paradigm” on a general level, but one that is substantive enough to be of practical meaning. There are three directions that seem to be the most promising:
the mineral organic as the gateway to the new generation of C-PC;
nanomodification as the new thrust in C-PC technology;
PCC as waste polymer product storage – paradoxically a new application area.
“Novelties in unexpected areas” are not included. The list may be short but it is not exhaustive!
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