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Cumulative heat evolution of the control, Na 2 CO 3 activated, and waterglass/NaOH activated mixtures (C, S, and W, respectively) over the initial 48 h as determined by isothermal calorimetry with an in situ mixing attachment. Inset Cumulative heat evolution over only the first hour. Units of the inset axes are the same as the larger figure, and are omitted for clarity
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Alkali activated slag shows considerable promise as an environmentally friendly alternative to binders produced from ordinary portland cement. The shrinkage behavior of alkali activated slags, however, is not well understood, and is a hurdle to widespread adoption. The use of pre-wetted lightweight aggre-gate-based internal curing to mitigate shrin...
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... use of the in situ mixing apparatus enabled quantification of the heat flow (Fig. 3) and cumulative heat evolution (Fig. 4) from the moment activating solution came in contact with slag or cement powder. Fig. 2 Compressive strengths of the control, Na 2 CO 3 activated, and waterglass/NaOH activated mixtures (C, S, and W, respectively) at ages of 3, 7, and 28 days with and without internal curing. All scales are equal. Error bars represent standard deviation ...
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Nowadays, there are many efforts to reduce CO2 emissions in the building industry, particularly through the use of some alternative binders to those based on Portland cement. One promising group of such binders includes binders based on alkali-activated slag (AAS). However, extensive drying, autogenous shrinkage and the associated cracking prevent...
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... Many researchers have conducted research to identify the complex and unclear contraction mechanism of AASC. It has been reported that the shrinkage behavior of AASC is affected by diverse and complex factors, such as humidity [32,36,37], the nature of raw materials [17,31,33], temperature [38,39], the drying history [40], the curing regime [41-44], pore size [33], the activator type and dosage [7,22,23,[45][46][47], aggregate properties [48,49], and the exposure period [50]. Additionally, experiments and research have been conducted to study contraction prediction models for various AACs [27,34,51]. ...
To reduce drying shrinkage of AASC mortar (AASM), mixed aggregate mixed with river sand (RS) and silica sand in three sizes was used to investigate the effect of the physical properties of mixed aggregate on shrinkage reduction. A mixture of river sand (0.2–0.8 mm), S1 (2.5–5.0 mm), S2 (1.6–2.5 mm), and S3 (1.21–160 mm) had river sand–silica sand mean diameter ratios (dr) of 7.68 (S1/RS), 3.75 (S2/RS), and 3.02 (S3/RS). The compressive strength and drying shrinkage characteristics of mixed aggregates according to fineness modulus, surface area, bulk density, and pore space were investigated. It had the highest bulk density and lowest porosity at a substitution ratio of 50%, but the highest strength was measured at a substitution ratio of 50% or less. High mechanical properties were shown when the fineness modulus of the mixed aggregate was in the range of 2.25–3.75 and the surface area was in the range of 2.25–4.25 m2/kg. As the substitution rate of silica sand increased, drying shrinkage decreased. In particular, the drying shrinkage of RS + S1 mixed aggregate mixed with S1 silica sand, which had the largest particle size, was the smallest. When silica sand or river sand was used alone, the drying shrinkage of the sample manufactured only with S1, which has the largest particle size of silica sand, was the smallest among all mixes. Compared to RS, at a 5% activator concentration, drying shrinkage was reduced by approximately 40% for S1, 27% for S2, and 19% for S3. At a 10% concentration, S1 showed a reduction effect of 39%, S2 by 28%, and S3 by 13%. As a result of this study, it was confirmed that the drying shrinkage of AASM could be reduced simply by controlling the physical properties of the aggregate mixed with two types of aggregate. This is believed to have a synergistic effect in reducing drying shrinkage when combined with various reduction methods published in previous studies on AASM shrinkage reduction. However, additional research is needed to analyze the correlation and influencing factors between the strength, pore structure, and drying shrinkage of AASM using mixed aggregate.
... For example, cracking caused by shrinkage stress and other durability problems limit the practical application of AAS in engineering (Neto et al., 2008;Chen et al., 2023;Wang et al., 1995;Collins and Sanjayan, 2000). To solve this key technical problem, many scholars (Ye and Radlińska, 2017;Chen et al., 2023;Kumarappa et al., 2018;Song et al., 2016;Sakulich and Bentz, 2013;Zhao et al., 2019) have conducted relevant research on this topic. Philleo (1991) proposed the concept of internal curing as early as 1991. ...
... Furthermore, the high shrinkage of AAS increases the risk of cracking, especially with water glass as an alkaline activator. Internal curing is thought to reasonably weaken the selfshrinkage produced by AAS mortar systems due to the volume change of pastes before and after the chemical reaction, and SAP is also considered to be the most potential and widely used internal curing agent (Sakulich and Bentz, 2013;Tu et al., 2018;Yang et al., 2023;Powers and Brownyard, 2003). The autogenous shrinkage of AAS paste was measured by NS-NC-12 channel cement mortar shrinkage tester with bellows length of 425 mm and outer diameter of 29 mm referring to ASTM C1698-19 (ASTM, 2014). ...
... The curves of heat flow of all mixtures exhibit two peaks. The first peak is generally produced by the wetting and the dissolution of the precursors (Sakulich and Bentz, 2013). Then after about 2~3 h of dormancy there is the second main peak, that is predominantly due to the formation of other phases, such as the aluminosilicate gel . ...
... Both drying shrinkage and autogenous shrinkage have been identified as important mechanisms in alkali-activated slags (Shi et al. 2006;Melo Neto et al. 2008). Autogenous shrinkage of AAS concretes has been observed to continue for a longer time and to reach higher ultimate values than ordinary PC (Sakulich and Bentz 2013;Orosz et al. 2019). Drying shrinkage increased with an increased dosage of alkali activator and with increased alkali modulus M s (SiO 2 =Na 2 O) of the sodium silicate (SS) activator (Melo Neto et al. 2008;Aydin and Baradan 2012;Humad et al. 2019;Orosz et al. 2019). ...
The construction of the future is moving in the direction of environmentally friendly materials and the use of various types of industrial byproducts and wastes. The use of blast furnace slag (BFS) for the production of concrete is one of those alternatives. In this study, pastes and concretes based on high-MgO BFS were alkali activated with 10% by weight sodium carbonate, sodium silicate, and a combination of both. Heat treatment and laboratory curing were applied. The results showed that heat treatment was effective at reducing the drying shrinkage of alkali-activated slag concretes and promoting high early strength. However, the sodium carbonate-activated slag concrete specimens showed a reduction in compressive strength at later ages. All concrete specimens tested exhibited high drying shrinkage; the highest values were for sodium silicate-activated concretes and the lowest were for sodium carbonate-activated concretes. All concretes tested showed very large creep, which was partly related to the small maximum aggregate size (8 mm) and the effects of carbonation. The carbonation depth after 12-24 months was significantly smaller for the heat-treated specimens and for concrete activated with sodium silicate. The carbonation process resulted in a more porous binder matrix, leading to long-term strength loss and increased creep, especially for sodium silicate-activated mixes.
... The phase in which the first peak appears is within 0.5 h and is defined as the induction period, as shown in Fig. 12 (a). Typically, the initial peak can be attributed to wetting and dissolution of cement and slag, which then gels into calcium silicate (i.e., C-S-H gels) and other phases (mainly aluminates) [64]. In this exothermic process, ettringite (AFt) is formed from gypsum-like material and the C 3 A in cement is hydrated. ...
The effect of replacing cementitious materials with different dosages of river sludge on the properties of the cement-slag binary-based geopolymer composites was investigated. The application of this research is the possibility of reusing river sludge into environment-friendly unburned bricks. The influence of nanomontmorillonite on the solidification of heavy metals in the matrix was also explored. Samples containing sludge were characterized by lower fluidity and compressive strength, but prolonged hardening time; at 60% replacement, the strength was equal to 8 MPa and the final setting time was 4.5 h. The sample including 0.4% NMt helps to improve strength thanks to its ability to partially fill the capillary pores and promote the degree of hydration. The pastes containing NMt have less dangerous heavy metals like Cu (II) and Cr (VI). The reaction products and the microstructure of the mixes with modified-NMt are exploited to understand the mechanisms at the basis of the findings.
... Many studies have been conducted on SAP incorporation into AAS paste, mortar and concrete. The autogenous shrinkage of sodium silicate-activated slag can be reduced by more than half, while sodium hydroxide and sodium carbonate-activated systems can even show expansion in the long term when SAP is present [29,45,46,54,56,58,111,158,159]. Experimental results from two example studies are shown in Figs. ...
... Kumarappa et al. [46] investigated the effect of LWA in AAS mortar and observed an autogenous shrinkage reduction of up to 50 % when 30 % of the aggregates were replaced by LWA. Sakulich and Bentz [159] also obtained a greatly reduced autogenous shrinkage of AAS mortar by using LWA, regardless of the liquid used for internal curing, i.e. water or alkaline solution. However, a reduced compressive strength was also observed for the LWA-containing mixtures [159]. ...
... Sakulich and Bentz [159] also obtained a greatly reduced autogenous shrinkage of AAS mortar by using LWA, regardless of the liquid used for internal curing, i.e. water or alkaline solution. However, a reduced compressive strength was also observed for the LWA-containing mixtures [159]. ...
This paper provides a critical review on autogenous shrinkage of alkali-activated slag (AAS). It is reported that AAS paste, mortar, and concrete generally show larger autogenous shrinkage than Portland cement (PC) counterparts. Self-desiccation is the main driving force of the autogenous shrinkage of hardened AAS, but other mechanisms also play roles, particularly at early age. Existing models developed for PC do not give satisfactory estimations of the autogenous shrinkage of AAS, unless the pronounced viscoelasticity of AAS is considered. The susceptibility of AAS concrete to extensive cracking is not necessarily high due to the effects of stress relaxation, but local creep can exacerbate the development of microcracks. Various strategies have been proposed to mitigate the autogenous shrinkage of AAS, but many exhibit side effects, e.g., strength reduction. Existing testing methods for autogenous shrinkage of PC seem applicable to AAS, but the starting time and test duration need to be reconsidered.
... They indicate that during the first few days, the total volume of the system remains constant or slightly increases for the mix lS and mix hS, respectively. The fact that no chemical shrinkage is predicted at earlyage is contradictory with the experimental results that can be found in the literature, but after a few days, the results are comparable to what can be found experimentally [9,76,[105][106][107]. The error in prediction Phase assemblage for mix lS (a) and mix hS (b) predicted by the thermodynamic model presented in [34]. ...
In this study, multi-scale experiments and analytical micro-mechanics based modeling are conducted to evaluate Young's modulus of alkali-activated slag (AAS) concrete. The evolution of volume fractions of phases is obtained using a thermodynamic model coupled with a kinetic model. Nano-indentation measurements indicate the existence of a soft and a hard matrix made of reaction products, independently of the mix tested. The homogenization model for Young's modulus is validated against results on paste and concrete with more than 95 % accuracy. Sensitivity analysis reveals Young's modulus of aggregates and of the soft matrix as the main influencing parameters.
... The effects of RA content and alkaline concentration on drying shrinkage in the RAC specimens are presented in Fig. 12. Drying shrinkage had increased significantly by the 7th day of curing due to the rapid hydration reaction between the GGBFS and alkaline solution (Huang et al., 2021;Sakulich and Bentz 2013). The RA mixtures exhibited higher drying shrinkage values than the control mixture, as shown in Fig. 12a. ...
The purpose of this study was to evaluate the mechanical properties of concrete specimens produced with recycled aggregate (RA) from construction demolition waste (CDW) based on alkaline activated slag-fly ash (AASF). The recycled aggregate concrete mixtures (RAC) were designed using DMDA method, with RA used as a 30%, 40%, and 50% partial replacement for natural aggregate (Category 1) and with Na2O doses of 4%–8% and modulus ratios of 0.6–1.4 (Ms = SiO2/Na2O; Category 2). The results showed that the inclusion of RA negatively affected the mechanical properties of RAC specimens, with recycled coarse aggregate exhibiting less of a negative effect than recycled fine aggregate. The concrete mixtures exhibited mechanical strength values of 20.7–35.9 MPa and UPV values of 3692–4200 m/s at 28 days of curing age. Concrete characteristics were significantly better in the mixtures produced using higher alkaline concentrations than in those produced using lower alkaline concentrations.
... Concrete is one of the most widely used materials in the construction industry and contributes a huge amount of carbon emission to global warming. This is mainly caused by the cement production which involves the thermal decomposition of calcium carbonates and other carbonates [1]. Therefore, it is crucial to find an alternative material to replace ordinary Portland cement (OPC). ...
... (1). ε autogenous = L aT − L fs L fs × 10 6 μm/m (1) where L aT is the length of the sample at the time of measurement, L fs is the length of the sample at the time of final setting. ...
... It was reported that the autogenous shrinkage of AAS can increase continuously during a 56-day recording period (4) and become about 5 times larger than that of OPC (14). In detail, the recorded autogenous shrinkage of AAS with various concentrations of activators (Na 2 CO 3 or NaOH/water glass) can be as high as 1.5% or 3.5% at 28 d, respectively (15). Ye et al. (16) found that AAS experiences substantial drying shrinkage despite the exposed relative humidity. ...
Alkali-activated slag (AAS) materials activated by NaOH or waterglass has been long-term criticized for the developed substantial shrinkage. To this regard, this paper explored MgO as both an activator and an expansive agent to prepare shrinkage-free AAS. The setting time, mechanical strength, pore structure, autogenous shrinkage, drying shrinkage, and hydration products of MgO-activated AAS were studied. Experimental results confirmed that MgO can effectively mitigate the autogenous shrinkage and drying shrinkage of AAS via the expansive deformation caused by Mg(OH)2. Generally, AAS with a higher dosage of MgO developed less shrinkages and refiner pore structures with more gel pores. An optimal dosage of 9% MgO is recommended to prepare AAS with near zero shrinkage and the highest flexural strength.
... The early SSC concrete has a high proportion of harmful holes due to its large water consumption per cubic metre. In addition, it involves the extensive curing method for traditional Portland cement concrete, which generally causes exfoliation of ash and sand on the concrete surface [101]. This is because CO 2 can easily migrate inward along a large number of harmful capillary pores; react with ettringite within a certain depth of the surface layer; generate calcium carbonate, gypsum dihydrate and aluminium hydroxide gel; and lose a lot of crystal water. ...
Cementitious material based on synergistic industrial wastes can be used as a new product for low-carbon transformation. It can aid in resource recycling and suitable consumption and utilisation of various industrial wastes. The proposed material can reduce a large amount of CO2 emitted during calcination in cement production and the decomposition of raw limestone. In addition, the material exhibits high durability and high resistance to corrosion in the marine environment that can further reduce CO2 emissions over the lifecycle of the carbon footprint of the building. Currently, many similar chemical kinetic processes and mineralogical reaction processes of particle migration and rebinding exist in the hydration and hardening reactions, service processes and durability evolution of different industrial waste cementitious systems for low-carbon production. The theoretical basis of preparing various low-carbon cementitious materials (LCCMs) with industrial waste systems is discussed herein, including the two theories of ‘complex salt effect’ and ‘isomorphic effect from tetrahedral coordination of silicon-oxygen’. Further research on LCCM is based on the theoretical foundation of ‘passive hydration kinetics’. Furthermore, this study presents the CO2 reduction potential of LCCM prepared using industrial wastes and provides future research directions in this regard.
