10 - Pozzolana and Pozzolanic Cements

Waste wood fly ash (WWFA) generated during wood chips combustion in a power plant does not have any application nowadays and is commonly disposed of or landfilled. Nevertheless, considering its composition and reactivity in the presence of calcium hydroxide, it is one of the promising materials that could be used as an active admixture for modification and partial replacement of lime in lime plasters. This solution seems to be a suitable step to both improve the properties of the traditional lime plaster and reduce carbon dioxide emissions. Therefore, this comprehensive study describes a wide range of properties of lime plaster with WWFA (up to 50 wt% lime replacement) as an active admixture. Compositions of studied plasters were firstly analyzed with the help of XRD, DSC, and SEM, and then the effect of WWFA on the physical, mechanical, hygric, and thermal properties was investigated. The obtained results showed that the application of WWFA led to lower total porosity, highly improved mechanical properties, higher thermal conductivity, and lower water transport capability, which could be attributed to its pozzolanic activity. The performed experiments fundamentally broadened the existing insufficient knowledge about the utilization of WWFA for lime-based plasters improvement. All tested lime-based plasters (with 10, 20, 30 and 50% lime replacement by WWFA) have a high potential for common use in practice, especially in the historical buildings renovation. The originality of this paper lies, among others, in using a specific type of fly ash (originating from waste wood, not coal) and in testing a wider range of characteristics and properties of designed lime-based plasters with WWFA with respect to their changes over time, which enables prediction of plasters' durability.

Preventing the indiscriminate disposal of wastes and reducing environmental pollution via the use of supplementary cementitious material cannot be over-emphasized. This research examines the characteristics of Recycled Concrete Powder (RCP) and its potential use as a partial replacement for cement in concrete production. Waste concrete was sourced and recycled, obtaining RCP. The RCP samples were characterized through various microscopic techniques. The effects of RCP on cement were examined on the rheological and mechanical properties by partially replacing it with 0–40 wt percentage (wt. %) of Ordinary Portland Cement (OPC) in 5 wt % increments. Lifecycle of the cement-blended RCP was assessed based on cradle-to-gate confinement by evaluating the Embodied Energy (EE) and Global Warming Potential (GWP). The sustainability and economic indexes were determined at 28 days compressive strength. The active presence of calcite, silica, alumina, and ferrite in RCP enhanced the microscopic properties of the RCP Blended Cement (RCPBC) mortar. The rheology and compressive strength of RCPBC mortar increased with increasing RCP content in the mix. However, about 25 wt % of RCP replacement in the mix was optimum to attain 75% of the strength activity index. The EE and GWP of RCP BC mortar dropped by 5–34% and 85–90% at 5–40 wt % RCP substitution compared to the control mortar. A replacement level of 25 wt % RCP substitution yielded the best economic and sustainable scores. Ultimately, RCP has demonstrated a sustainable material and the findings can help achieve cleaner production, environmental protection, and sustainability.

A reduction in cement consumption can be achieved through the use of supplementary cementitious materials (SCMs). In addition, the utilization of more than one SCM can show a beneficial synergic performance. In this paper, a combination of calcium aluminate cement, alumina admixtures and one other type of SCM was investigated. Namely: microsilica, ferrite powder, ceramic dust, calcined shale and sintered mullite were employed. The phase compositions of the designed binders were primarily characterized by XRD, XRF, DSC and SEM. Subsequently, the basic physical and mechanical properties as well as thermal expansion of the ternary binder-based composites up to 1400 °C were determined. The results revealed the synergic performance of used components. Calcined shale and ceramic powder were the most promising admixtures, exhibiting compressive strength of 80 MPa at room temperature and 117 and 128 MPa for ceramic powder and calcined shale, respectively, after exposure to 1400 °C.

In this paper an overview is presented on the use of diatomaceous earth (DE) as a partial substitute for binder and fine aggregate in mortars. For this purpose, this paper was divided into two sections. In the first one, concepts related to physical, chemical and microstructural properties of DE, as well as results of previous studies about its reactivity used in different construction materials (cement, concrete, mortar, bricks, phase change materials etc.) were summarized and discussed. In the next section, the effects of using DE on the fresh, hardening and durability properties of cement and lime-based mortars were discussed. In general, the results suggest that increasing DE content may reduce mortar performance due to the high porosity of its particles. However, this deficiency was observed for DE contents higher than 20%, which, however, can be compensated for by using superplasticizer additives or by volumetric dosage instead of by weight one. This critical value of up to 20% of DE was calculated using T² statistical on the scores of principal components analysis obtained from the results collected from publish manuscripts. Nevertheless, the results of this review research may contribute to provide information on an under-explored alternative source of supplementary cementitious materials (SCMs) and therefore help mitigate the negative effects generated by the cement industry and assist in the production of mortars with a lower carbon footprint that can play an important role in the thermal behavior of buildings.

Common clay deposits contain a variety of minerals that provide low and unpredictable reactivity even after calcination. This study aims to enhance the reactivity of such low-grade clay via alkali thermal fusion, where clay was co-calcined with different dosages of NaOH to achieve superior reactivity. The effects of such co-calcination on the formation of reactive aluminosilicates were monitored using high-temperature in-situ X-ray Diffraction (XRD). Additionally, the role of different alkali dosages on the characteristics of the calcined clays was studied using ex-situ XRD, FTIR, ICP-OES, and ²⁹Si NMR. The co-calcination process significantly enhanced the Al and Si dissolution from the calcined clays, which subsequently improved their pozzolanic properties. All of the alkali-fused SCMs satisfied the modified strength activity index (SAI) requirement and the lower dosages of alkali-containing samples (5 % NaOH) showed 50 % reduction in expansion due to alkali silica reaction.

In the repair of historical masonry and listed buildings, the requirements for compatibility and preservation of the original appearance and cultural and historical value of the rehabilitated structure are often discussed. In particular, technical, technological and material compatibility is often addressed by engineers and conservation professionals and the resulting solution often involves finding a compromise between an ideal, technically functional solution and preserving the historic value of the building for future generations. The material solution of mortars for repair of historical structures is based on the application of a suitable binder and porous filler, which allows achieve their high porosity, water vapor permeability, sufficient strength and durability. Obviously, there is no single ideal material solution for these mortars and it is always necessary to take into account the current state of the reconstructed structure and the composition and properties of the original materials in their design and application. The aim of the research presented here was to design and experimentally assess rendering and plastering mortars based on lime hydrate and natural hydraulic lime partially lightened with chalcedonite as a porous aggregate. The results of the material tests were compared with criteria imposed in WTA recommendation 2-9-03.2020/E. Chalcedonite was used as an alternative filler to silica sand and its application enabled the required values of porosity, compressive strength, water absorption coefficient and water vapor diffusion resistance factor to be achieved. The lightened plasters also showed increased hygroscopicity, low thermal conductivity and increased resistance to salt crystallization. Depending on the binder used and the demanded mechanical strength, the examined mortars thus represent materials applicable in the repair of damp and saline masonry of historical buildings.