Supplementary Cementitious Materials Content Research Articles

Valorization of industrial wastes for sustainable cement-based materials with enhanced chloride binding

Improving the chloride binding capacity of cement-based material can effectively slow down the corrosion of steel bars in concrete. This study investigated the valorization of two industrial wastes, carbonated sintering red mud (CSRM) and bauxite tailings (BT), as supplementary cementitious materials (SCMs) to enhance the chloride binding capacity of cement-based materials. CSRM and BT were incorporated separately and in combination to prepare cement paste mixtures, replacing 10–30 % of ordinary Portland cement. The bound chloride contents were determined, and the hydration products were characterized using X-ray diffraction and thermogravimetric analysis. Both CSRM and BT promoted the formation of Friedel's salt (FS) through increased aluminum dissolution and conversion of monocarbonate/monosulfate phases. In the early ages, the synergistic effect of CSRM and BT resulted in the highest FS content. At later ages, BT demonstrated superior chloride binding due to its high alumina content facilitating continued FS formation. Furthermore, the adverse effect of CSRM on the composite system was less than that of BT. At 28d age, when the SCMs content was 30 %, the compressive strength of cement-BT system was 34.5 % lower than the control, while the compressive strength of cement-CSRM system was only 20.9 % lower than the control. The findings highlight the potential of valorizing CSRM and BT as sustainable SCMs for developing chloride-resistant cement-based materials.

The improvement on calcium leaching resistance of high SCMs content cement in ammonium chloride solution using particle gradation technique

Particle gradations of Portland cement (PC), fly ash (FA), and blast furnace slag (BFS) were optimized to improve the calcium leaching resistance of blended cement with high contents (up to 70%)of supplementary cementitious materials (SCMs). The results showed that optimized blended cement showed refined initial pore volume distribution, reduced portlandite (CH) content, finer CH macrocrystals and enhanced stability of C-(A)-S-H gel. Consequently, it displayed exceptional calcium leaching resistance with reduced losses in mechanical performance, mass and pore degradation after calcium leaching. Blended cement with 30% PC (D50 = 14.46 μm), 30% FA (D50 = 10.94 μm), 20% BFS (D50 = 10.52 μm), 13% BFS (D50 = 5.31 μm) and 7% BFS (D50 = 4.71 μm), showing compressive strength retention rate of 79.05% and mass loss rate of 1.64%, was suggested as viable choice for calcium leaching resistant concrete.

Effect of Polymer/Nano-Clay Coatings on the Performance of Concrete with High-Content Supplementary Cementitious Materials under Harsh Exposures.

In recent concrete research, a novel category of coatings has emerged: polymers/nanoparticles blends. The efficacy of such coatings warrants extensive examination across various concrete mixtures, particularly those incorporating high-volume supplementary cementitious materials (SCMs) to mitigate carbon footprints, an industry imperative. This study used three vulnerable concrete mixtures to assess the effectiveness of ethyl silicate and high-molecular-weight methyl methacrylate blended with 2.5% and 5% halloysite and montmorillonite nano-clay. Findings from physical, thermal, and microstructural analyses confirmed vulnerabilities in concretes with a high water-to-binder ratio (0.6) under severe exposure conditions, notably with high SCM content (40% and 60% fly ash and slag, respectively). Neat ethyl silicate or high-molecular-weight methyl methacrylate coatings inadequately protected those concretes against physical salt attacks and salt-frost scaling exposures. However, the incorporation of halloysite nano-clay or montmorillonite nano-clay in these polymers yielded moderate-to-superior concrete protection compared to neat coatings. Ethyl silicate-based nanocomposites provided full protection, achieving up to 100% improvement (no or limited surface scaling) against both exposures, particularly when incorporating halloysite-based nano-clay at a 2.5% dosage by mass. In contrast, high-molecular-weight methyl methacrylate-based nano-clay composites effectively mitigated physical salt attacks but exhibited insufficient protection throughout the entire salt-frost scaling exposure, peeling off at 15 cycles.

Synergistic effect of recycling waste coconut shell ash, metakaolin, and calcined clay as supplementary cementitious material on hardened properties and embodied carbon of high strength concrete

Researchers are investigating eco-friendly binders like coconut shell ash (CSA), metakaolin (MK), and calcined clay (CC) as supplementary cementitious materials (SCM) in high-strength concrete (HSC). Abundantly available as industrial or agricultural waste, these materials, when combined with Portland cement (PC), offer synergistic benefits. This not only improves concrete performance but also addresses waste disposal issues, presenting a sustainable and environmentally friendly solution for long-term use in HSC production. However, this study performed on fresh and mechanical characteristics of HSC blended with CSA, MK, and CCA alone and together as SCM after 28 days of curing. A total of 504 samples of standard concrete were cast and the cubical samples were tested to achieve the targeted compressive strength about 80 MPa after 28 days. The experimental results indicated that the rise in tensile, flexural and compressive strengths of 9.62%, 8.27%, and 10.71% at 9% of CSA, MK, and CC as SCM after 28 days of curing. As SCM content increases, the density, porosity and water absorption of concrete decrease. Moreover, the workability of fresh concrete is getting reduced when the concentration of SCMs increases in HSC. In addition, the concrete's sustainability assessment revealed that employing 18% MK, CC, and CSA as SCM reduced carbon emissions by approximately 11.78%. It is suggested that using 9% CC, MK and CSA together in HSC yields the best results for practical applications in civil engineering.

Use of cellulose nanomaterials in cementitious composites reinforced with basalt/polymer pellets for repair of concrete

Using cellulose nanomaterials (nano-crystalline [NC] and/or nano-fibrillated [NFC] cellulose) with a high content of supplementary cementitious materials and special class of basalt fiber/polymer (BFP) pellets could produce sustainable and resilient composites for a suite of infrastructure applications. Hence, this study investigated the development of cementitious composites comprising high content slag (50% as cement replacement), BFP (4.5% by volume), NFC ranging from 0 to 0.5% (addition to the mass of the binder) and NC (0 to 0.1% addition to the mass of the binder) to prepare multiple formulations without/with nano-silica (reference nanomaterial) for repair/overlay applications of concrete flatwork. An integrated experimental program including constructability, mechanical capacity, and durability properties as well as compatibility with substrate concrete was conducted. Findings of these tests were corroborated with thermal and microstructural tests to evaluate the hydration/pozzolanic development and pore structure features. The overall results indicated that the development of high-cementitious composites with cellulose nanomaterials is possible, as they achieved balanced behaviour in terms of workability, hardening rates, high early- and later-age compressive strengths, high ductility, improved durability, and superior thermal and elastic integrity/compatibility with the parent/normal concrete. Thus, they may present an attractive option for repair and overlay applications of concrete flatwork.

Carbonation resistance of sustainable self-compacting concrete with recycled concrete aggregate and fly ash, slag, and silica fume

This study focused on the problem of recycling construction and demolition wastes as well as industrial waste by-products into sustainable concrete materials. By combining addition of three different industrial waste by-products, an environmentally friendly recycled aggregate self-compacting concrete (RA-SCC) mix was put forward. Carbonation resistance and microstructure of SCC incorporating high volumes of industry by-products and recycled aggregates were studied in this paper. A total of 9 RA-SCC with 50%, 75% supplementary cementitious materials (SCMs) and different SCM combinations were prepared, which consist of binary mix with fly ash (FA), ternary mix with FA and ground granulated blast-furnace slag (GGBS), and quaternary mix with FA, GGBS, and silica fume (SF). An exposure period of 3, 7, 14, and 28 days was adopted for accelerated carbonation tests. The test results indicate that, as RCAs content increased, RA-SCC carbonation depth increased. The carbonation depth of SCC with 100% RCAs increased by 49.35% compared to that of normal SCC. In addition, carbonation resistance of RA-SCC mixes with a given compressive strength decreased with increasing SCM content. However, the loss in carbonation resistance was greatly mitigated by the combined addition of different SCMs, on account of the substitution of cement with industrial by-products and natural aggregates with RCAs. The combined addition of different SCMs enhanced the carbonation resistance of RA-SCC mixes. The test results were validated through microstructural analysis using scanning electron microscopy (SEM), and X-ray diffraction (XRD). A comparison between predictions calculated using existing models and measured carbonation depth was implemented. By taking into account the effect of RCAs and SCMs, a modified carbonation model in conjunction with fib carbonation model was put forward.

Time-depth dependent chloride diffusion coefficients of self-compacting concrete

Chloride attack severely impacts the performance of reinforced concrete. The total and free chloride ion concentrations (CICs) of self-compacting concrete (SCC) prepared with three supplementary cementitious materials (SCMs) - fly ash (FA), blast furnace slag (BS), and silica fume (SF) – were measured through the accelerated salt immersion tests. The apparent chloride diffusion coefficients (CDCs) at any exposure time and erosion depth were calculated using the Boltzmann-Matano method. The influence of the type and content of SCMs, the water-binder ratio (W/B), and the type of salt solution on CICs and CDCs were investigated. Both introducing SCMs and reducing W/B effectively reduced the CIC. The SCM that most effectively reduced CIC was SF, followed by BS and then FA. Free CICs were reduced to a greater degree than total CICs in FA and BS concrete, but the opposite was true for SF concrete. Presence of calcium chloride in salt solution increased total CICs while reducing free CICs. Apparent free CDC dropped over exposure time and initially increased with erosion depth but eventually stabilized. A model of apparent free CDC considering the time-depth dependence was created, which shows that time reduction factors of CDC is larger in SCM-containing SCC than in control SCC.

Designing sustainable high-strength self-compacting concrete with high content of supplementary cementitious materials

A sustainable and green approach to concrete mix design is fundamental for the construction sector in terms of reducing carbon dioxide ( CO 2 ) emissions and conserving non-renewable natural resources. This article proposes a novel mix design method for sustainable high-strength self-compacting concrete (HSSCC) based on rheological and mechanical properties with the aim of reducing cement content in such mixes. HSSCC mixes were designed using ground granulated blast furnace slag (GGBS) and fly ash to replace up to 40% of the cement content and tested for target compressive strengths ranging between 70 and 100 MPa. The proposed design method was numerically programmed to provide straightforward and realistic guidance in the form of design charts and verified through the design and production of sixteen HSSCC mixes consisting of varying sand-to-aggregate ratios (S/A). All mixes satisfied the self-compacting concrete criteria in the fresh state and achieved the targeted viscosity and compressive strength values. The effects of S/A and paste-to-solid (P/S) ratios on the rheological properties were evaluated. The experimental results demonstrated that the proposed mix design method could produce HSSCC with excellent fresh and mechanical characteristics while being eco-efficient with respect to CO 2 emissions and cement consumption.

Comparative analysis of quaternary blended self-compacting concrete (QBSCC) mixes incorporating induction furnace slag (IFS) and crushed stone aggregate: A performance study

This study explores using Induction Furnace Slag (IFS) as aggregate in Quaternary Blended Self-Compacting Concrete (QBSCC) mixes. The experimental work consists of two stages. Stage I focuses on determining the optimal QBSCC mixes, aiming to develop environmentally friendly Self-Compacting Concrete (SCC) by utilizing different types and ratios of cementitious materials. A total of 27 QBSCC mixes were prepared with a reference SCC mix consisting of 100% ordinary Portland cement (OPC), are prepared considering water binder (w/b) ratio of 0.4. The quaternary blended mixes are created by combining OPC, class F Fly Ash (FA), Silica Fume (SF) and Ground Granulated Blast Furnace Slag (GGBFS). The replacement ranges for SF are set between 2.5% and 7.5% in increments of 2.5%, for FA between 10% and 20% in increments of 5%, and GGBFS between 30% and 50% in increments of 10%. In stage II, the optimized QBSCC mixes are further enhanced by incorporating IFS, the properties in the fresh state such as slump flow, V-funnel, L-box, and J-ring tests are conducted for all SCC mixes, all of which comply with the EFNARC guidelines. The mechanical characteristics studied, includes compressive strength (cube and cylinder), split tensile strength (at 3, 7, 28, and 56 days), flexural strength (at 28 and 56 days), elastic modulus, shear strength and pull-out bond strength (at 56 days) are evaluated. It is noted that the hardened properties of SCC mixes containing IFS exhibit slightly higher values compared to crushed stone aggregate SCC mixes. Furthermore, an increase in Supplementary Cementitious Material (SCM) content in QBSCC mixes leads to a decrease in the hardened properties, irrespective of the kind of aggregate used. The QBSCC mixes identified as SCC57.5/42.5, SCC52.5/47.5, and SCC47.5/52.5 are determined to be the preferred blends for producing Self-Compacting Concrete (SCC). Remarkably, Induction Furnace Slag (IFS) can be utilized as both fine and coarse aggregate, completely replacing conventional aggregates, regardless of the content of supplementary cementitious materials (SCM). This finding highlights the notable effectiveness of IFS as a replacement material in SCC production.

AI-Assisted optimisation of green concrete mixes incorporating recycled concrete aggregates

Maximising the content of supplementary cementitious materials as a partial replacement for Portland cement and using recycled concrete aggregates as a full or partial replacement for coarse aggregates are among the widely adopted strategies in the design of green concrete. However, the synergetic implications of adopting both approaches on concrete properties add complexity to the design of green concrete mixes. This paper proposes a novel AI-based multi-objective optimisation framework addressing the lack of a systematic method to formulate these concretes and solves the common multi-objective mix design problems. The framework is developed for the mix proportioning of green concrete mixes containing recycled concrete aggregates and commonly used supplementary cementitious materials while considering the desired compressive strength. The proposed optimisation model leverages a dataset of about 2,120 mixes and employs an extreme gradient boosting machine to model the compressive strength requirements as a mechanical constraint throughout the optimsiation process. Moreover, a set of key environmental objectives, including minimising global warming, acidification, fossil fuel depletion potentials, and the cost of production, are targeted. The effectiveness of the framework is validated through case studies across different strength ranges. The results indicate a significant improvement in environmental sustainability indicators, including a 19.6% and 21.6% reduction in global warming and acidification potentials, besides considerable cost savings of up to 23.7% without compromising the mechanical performance of concrete.

The Study of the Effects of Supplementary Cementitious Materials (SCMs) on Concrete Compressive Strength at High Temperatures Using Artificial Neural Network Model

In this study, an artificial neural network (ANN) model was developed to predict the compressive strength of concrete containing supplementary cementitious materials (SCMs) at high temperatures. For this purpose, 500 experimental results were collected from the available literature. The effective parameters in the model are the volumes of coarse and fine aggregates, water, cement, coarse-aggregate type, percentage SCMs as the cement replacement, temperature levels, and test methods. The proposed ANN model was developed at a correlation coefficient of 0.966. A parametric study was conducted to evaluate the impact of the combined effects of input parameters (aggregate types and SCM content) on the relative compressive strength of concrete at high temperatures. It was shown that siliceous aggregate has a better performance by producing stronger bonds with cement paste than calcareous aggregates. The optimum SCM contents depend on the aggregate types. The optimum silica fume (SF) content for concrete with a water-to-binder ratio of 0.6 subjected to high temperatures is 8% and 3% for siliceous and calcareous concrete, respectively. The analysis of the ANN model has provided a conclusive understanding of the concrete behaviour at high temperatures.

Effect of sodium sulfate activation on the early age behaviour and microstructure development of hybrid cementitious systems containing Portland cement, and blast furnace slag

Alkali activation may help to increase the early strength and reduce the setting time of mixtures with high contents of supplementary cementitious materials (SCMs). In this research, the effect of sodium sulfate activator on reaction kinetics, compressive strength and pore structure of hybrid systems produced with 70 wt% ground granulated blast furnace slag (GGBFS) and 30 wt% Portland cement (PC) was determined. The setting time was shortened by adding sodium sulfate, but increasing the dose above 3 wt% did not influence it drastically. In-situ XRD measurements revealed an increasing ettringite formation within the first 2 days of hydration. A greater reaction of the GGBFS resulted in a pore refinement of the mortars studied and consequently raised the early age compressive strength. The assessment of a convenient dosage of activator was based on both technological and environmental parameters. The contribution of PC and GGBFS to compressive strength was “decoupled”.

Mechanical properties and brittleness of concrete made by combined fly ash, silica fume and nanosilica with ordinary Portland cement

<abstract> <p>This paper introduced a new concrete composites made by quaternary binder by partially replacing ordinary Portland cement (OPC) with different percentages of supplementary cementitious materials (SCMs). The motivation is to reduce our dependency on OPC to reduce CO<sub>2</sub> emission and carbon foot print. As the main substitute for the OPC, siliceous fly ash was used (FA). Moreover, silica fume (SF) and nanosilica (nS) were also used. This study utilized the following contents of SCMs used: 5% of nS; 10% of SF; 0, 15, and 25% of FA. During examinations the main mechanical properties of concrete composites, i.e. compressive strength (<italic>f</italic><sub>cm</sub>) and splitting tensile strength (<italic>f</italic><sub>ctm</sub>) were assed. The brittleness of these materials was also analysed. Based on the conducted studies, it was found that concrete composite based on quaternary blended cements, of series Mix3, has shown the best results in terms of good strength parameters, whereas the worst mechanical parameters were characterized by concrete of series Mix4. On the other hand, concrete including only SF and nS (Mix2 series) were characterized by the greatest brittleness. It was observed that <italic>f</italic><sub>cm</sub> of concrete composites for series Mix2, Mix3, and Mix4 increase of 41%, 48%, and 31% respectively compared with the concrete without additives, i.e. series Mix1. In addition, <italic>f</italic><sub>ctm</sub> also increase of 39%, 47%, and 30%, respectively, for the three series mentioned above, compared with the control concrete. Concrete of series Mix3, with high mechanical properties and demonstrating the features of quasi-plastic material, i.e. having lower brittleness, can be used in concrete and reinforced concrete structures subjected mainly to dynamic and cyclic loads. Therefore, it can be used, in the construction of foundation structures for machines and other types of structures in which the above-mentioned loads are dominant.</p> </abstract>

Fresh and hardened properties of recycled plastic fiber reinforced self-compacting concrete made with recycled concrete aggregate and fly ash, slag, silica fume

This study addressed the issue of recycling of waste plastic, industry by-products and waste concrete into sustainable concrete materials, which aims to produce a green and environmental-friendly self-compacting concrete (SCC). A novel and sustainable approach was proposed by combined inclusion of supplementary cementitious materials (SCMs) and recycled plastic fibers (RPFs), which was expected to improve the workability, mechanical properties and durability of recycled aggregate SCC (RA-SCC) simultaneously. This study firstly presents a deep insight into the benefits of the coupling effect of waste plastic fibers and SCMs on the fresh and hardened properties of recycled aggregate SCC mixes. Four series, 17 RPF reinforced RA-SCC (RPF-RA-SCC) were prepared by substantially substituting natural aggregates with recycled concrete aggregates and cement with SCMs, as well as reinforced with RPFs resulting from cutting waste plastic bottles. Fresh properties, including filling ability, cohesiveness, passing ability, segregation resistance and hardened properties, in terms of compressive, elastic modulus and flexural strength were measured. The effect of RCA content (50%, 100%), SCM content (50%, 75%) and different combination type, RPF content (0.5%, 1.0%, 1.5%) on the fresh and hardened properties of RA-SCC mixes was analyzed. The coupling effect of RPFs and SCMs was analyzed in detail. Microstructure analysis using scanning electron microscope (SEM) was conducted to study the microstructure characteristic. The test results indicated that the addition of RPFs impaired the workability. However, the inclusion of SCMs greatly improved the fresh properties and all RPF-RA-SCC mixes exhibited superior workability. The combined addition of RPFs and SCMs resulted in an excellent coupling effect and leaded to a notable improvement on the mechanical properties. The benefits of combined addition of SCMs and RPFs are higher than the sum of the benefits obtained through individual inclusion of SCMs and RPFs. • A sustainable approach was proposed by combined inclusion of SCMs and waste plastic fibers. • Fresh and hardened properties were simultaneously improved by combined addition of SCMs and waste plastic fibers. • The addition of SCMs increased the pull-out and bond strength of waste plastic fibers. • Combined addition of RPFs and SCMs result in excellent coupling effect. • Combined addition of RPFs and SCMs result in additional improvement in the net gain.

A long-term study on structural changes in calcium aluminate silicate hydrates

Production of blended cements in which Portland cement is combined with supplementary cementitious materials (SCM) is an effective strategy for reducing the CO2 emissions during cement manufacturing and achieving sustainable concrete production. However, the high Al2O3 and SiO2 contents of SCM change the chemical composition of the main hydration product, calcium aluminate silicate hydrate (C–A–S–H). Herein, spectroscopic and structural data for C–A–S–H gels are reported in a large range of equilibration times from 3 months up to 2 years and Al/Si molar ratios from 0.001 to 0.2. The 27Al MAS NMR spectroscopy and thermogravimetric analysis indicate that in addition to the C–A–S–H phase, secondary phases such as strätlingite, katoite, Al(OH)3 and calcium aluminate hydrate are present at Al/Si ≥ 0.03 limiting the uptake of Al in C–A–S–H. More secondary phases are present at higher Al concentrations; their content decreases with equilibration time while more Al is taken up in the C–A–S–H phase. At low Al contents, Al concentrations decrease strongly with time indicating a slow equilibration, in contrast to high Al contents where a clear change in Al concentrations over time was not observed indicating that the equilibrium has been reached faster. The 27Al NMR studies show that tetrahedrally coordinated Al is incorporated in C–A–S–H and its amount increases with the amount of Al present in the solution.

Long‐term behavior of sustainable self‐compacting concrete with high volume of recycled concrete aggregates and industrial by‐products

AbstractThe addition of recycled concrete aggregates together with industrial by‐products for the concrete production is an effective solution to the environmental problems in terms of excess waste materials and massive nonrenewable natural resources consumption. This article investigates the long‐term behavior and microstructure of sustainable self‐compacting concrete (SCC) by substantially substituting natural coarse aggregate with recycled coarse aggregates (RCA) and cement with supplementary cementitious materials (SCM). The influences of RCA and SCM content as well as SCM combination type (fly ash, ground granulated blast furnace slag and/or silica fume) on the mechanical properties and long‐term deformation of recycled aggregate SCC (RA‐SCC) were assessed in detail. Furthermore, scanning electron microscope and x‐ray diffraction were implemented to justify the reasons for improvement on mechanical properties and long‐term behavior of RA‐SCC. The results indicate that the addition of RCA reduces the compressive strength and elastic modulus of RA‐SCC, and increases the creep and shrinkage deformations. However, incorporating SCM with a combination of fly ash, ground granulated blast furnace slag and silica fume compensates for the detrimental effect of RCA and makes considerable improvement in strength and reduction in the long‐term deformations. Microstructure analysis confirms the reasons of improvement, which is mainly attributed to the addition of SCM by adopting a combination type, resulting in a more compact microstructure such as stronger interfacial transition zone. Based on the experimental results, the correction factors of RCA and SCM were introduced in conjunction with fib Model Code 2010 model to evaluate the creep coefficient of RA‐SCC.

Geopolymer synthesized from electrolytic manganese residue and lead-zinc smelting slag: Compressive strength and heavy metal immobilization

In order to follow the growing trend towards waste re-utilization and clean production, geopolymers were synthesized to immobilize Pb2+ and Zn2+ by simultaneously using electrolytic manganese residue (EMR) and lead-zinc smelting slag (LZSS) as raw aluminosilicate materials. Different contents of supplementary cementitious materials (i.e., blast furnace slag, sodium aluminate and silica-gel powder) were respectively employed to study the influences of Ca, Al and Si on compressive strengths of geopolymers. Moreover, the geopolymers can be used to immobilize heavy metals including Pb and Zn. The effects of heavy metals on compressive strength and leaching concentration were explored. Results showed that, geopolymers with 1% Pb(NO3)2 loading had a highest 7-day compressive strength of 28.5 MPa and a low heavy metal leaching concentration below the limit (total Pb < 5 mg/L, total Zn < 100 mg/L). Proved by XRD, FTIR, SEM-EDS, XPS analyses and theoretical calculation, the immobilization of Pb/Zn in EMR/LZSS based geopolymers was realized by physical encapsulation and chemical bonding. The proposed technology can be potentially used to convert Pb/Zn-containing solid wastes into less hazardous or nonhazardous solids for environmentally acceptable construction applications.

Exploring machine learning to predict the pore solution composition of hardened cementitious systems

This study explores machine learning (ML) algorithms to predict the pore solution composition of hardened cementitious systems produced with Portland cement (PC) and supplementary cementitious materials (SCM). Literature data on pore solution compositions for different cementitious systems was collected and compiled in a comprehensive database containing >300 entries with >80 features. Improved decision tree regressors were applied to the database. It was found that the trained ML models were capable of predicting OH−, Na+, and K+ concentrations reliably (75–90 % of predicted systems within 25 % relative error). Ca2+ and sulfur species had lower prediction accuracy. The silica content of SCM, the alkalis content of PC, and the SCM replacement level were identified as important features in determining the ion concentrations. When applied to this database, ML performed better than conventional, theory-based prediction models. Thus, ML models are a promising, complementary technique to determine pore solution compositions.

Influence of calcined medium grade clay on the properties of Portland cement pastes

ABSTRACT In the recent decades, the composition of Portland cements has undergone significant changes related to an increase in the range and content of supplementary cementitious materials following development of composite and multicomposite cements. The development of these binders that meet the requirements of sustainability requires the expansion and adaptation of the mineral resource base of cement industry to the production of low-emission binders with a gradual decrease of resource and energy intensities. Efforts to find the widespread sources of pozzolans providing high reactivity and physical–chemical stability have led to intensive studies on thermally treated clays of various chemical–mineralogical composition and their industrial adoption. Due to scarcity and high cost of kaolin clays, great attention is given to medium- and low-grade clays. This article reports on a study to evaluate the effect of calcined clay with 52% of clay minerals on the properties of fresh and hardened pastes, in particular on the resistance to sodium sulfate and nitric acid attacks. The reaction products assemblage of the blended Portland cement pastes was investigated by XRD and thermal analyses. The hardened Portland cement pastes incorporated with thermally treated clay demonstrated better durability performance compared to reference ones.

Autogenous shrinkage of fly ash and ground granulated blast furnace slag concrete

Supplementary cementitious materials (SCMs) are widely used to reduce the cement content to achieve economic and environmental objectives. As a result, understanding the shrinkage of blended cement-based concrete is essential. In total, 21 concrete mixes were produced with type general purpose cement and with cement replacements of 30% by fly ash, 40% and 60% by ground granulated blast furnace slag (GGBFS). The concrete compressive strength ranged from 25 MPa to 100 MPa. Experimental results were also compared with the predictions by models. Additional tests on pastes with the same SCM content were conducted to investigate both autogenous and chemical shrinkage in relation to their time-dependent pore structure refinement. For concretes with strength below 50 MPa, no significant difference in autogenous shrinkage could be observed between the different blends up to 28 days. However, the autogenous shrinkage of GGBFS concrete increased significantly after 28 days, being about 50% higher than all other concretes at 100 days. This late increase in autogenous shrinkage between 28 and 100 days can be attributed to pore refinement processes. No clear difference was observed for GGBFS concretes with strength greater than 50 MPa. Autogenous shrinkage of fly ash concretes was overall equivalent to that of reference concretes.