Final Setting Time Research Articles

Effect of liquid-solid ratio on metakaolin-based geopolymer binder properties

AbstractThis article aims to achieve the hardening of geopolymer binder-based metakaolin under the same setting time and hardening temperature as traditional cement. It studied the hardening of the geopolymer binder-based metakaolin at two temperatures of 60 °C and room temperature using different liquid-to-solid ratios of 0.8, 0.95, and 1.1. The bulk density, compressive strength, sitting times, thermal conductivity, and microstructure were measured for geopolymer binders. Based on the specified range for cement characteristics, the geopolymer binder was solidified at room temperature, utilizing a liquid-to-solid ratio of 0.8 to achieve optimal results stratified according to the cement's ideal characteristics. It had a bulk density of 1.264 g cm−3, compressive strength of 19.12 MPa, initial setting time of 288 min, final setting time of 358 min, and thermal conductivity of 0.49 W m−1 K.

An investigation into the microstructural evolution and shrinkage control in internally cured mortars with milkweed fibres

This study presented a significant advancement in the use of Milkweed (MW) fibres as internal curing agents in low water-to-cement (w/c) cementitious materials. The research focused on how different pre-treated MW fibres, with different composition, can impact internal curing efficacy in reducing autogenous shrinkage of cement mortars. In addition, the hydration behaviour and microstructural development were revealed using a series of tests including setting time, compressive strength, flexural strength, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA/DTG). A key finding of this study is the remarkable reduction in autogenous shrinkage, with using 0.1 % wt. pre-treated MW fibres leading to up to 28 % reduction at 7 days, compared to plain mortars. Furthermore, internal curing effect resulted in narrowing the compressive strength gap between the reference mixes and those with pre-treated MW fibres in the later stages of hydration. It was also found that the removal of hemicellulose through hybrid treatment can reduce the delay in the final setting time of cement from 45 minutes to 18 minutes. Additionally, while the incorporation of N- and HT-treated MW fibres had negligible effects on drying shrinkage, the inclusion of HY-treated MW fibres led to a 15 % increase in drying shrinkage at 7 days. This difference in behaviour was attributed to the presence of lignin in N- and HT-treated fibres. Lignin was found to play a crucial role in influencing the drying shrinkage, microstructural development, and mechanical properties of MW fibre-incorporated cementitious mixes. Acting as a protective barrier, lignin shielded the MW fibres from cement infiltration into their lumina. Moreover, it served as both a physical and chemical barrier, reducing moisture transport through the capillary network during drying. In conclusion, this study demonstrated the potential of using pre-treated MW fibres as internal curing agents to effectively reduce autogenous shrinkage, with minimal compromise in terms of the compressive strength of cementitious composites.

Hardening properties, water resistance and associated micro-mechanism of nano-modified calcium sulphoaluminate cement

Calcium sulphoaluminate cement (CSA) is considered a sustainable alternative to traditional Portland cement to reduce CO2 emissions. To further improve the hardening properties and water resistance of CSA and advance its extensive special engineering application, nanoparticles including nano-SiO2 (NS), nano-MgO (NM) and nano-Al2O3 (NA) were used as nano-modifiers for CSA. The effects of nanoparticles dosage on the setting time, compressive strength and water resistance of nano-modified CSA were experimentally evaluated, and the micro-mechanisms were also clarified by conducting X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TG) tests. The results showed that incorporating nanoparticles into CSA obviously shortened the initial and final setting times. The appropriate addition of nanoparticles effectively enhanced the compressive strength of CSA, and the optimum dosages of NS, NM, and NA were respectively determined to be 0.5%, 1.0%, and 0.5%. Water immersion decreased the bonding strength of CSA, and adding nanoparticles can effectively weaken this water-induced deterioration effect. Under water immersion environment, the optimum dosages of nanoparticles would be increased to obtain the highest residual water immersion strength and minimum strength loss rate. The generation of ettringite was mainly responsible for the compressive strength and water resistance improvements of nano-modified CSA. The hydration process of nano-modified CSA was clarified and the corresponding micro-mechanism model was proposed. Furthermore, the benefits and challenges of using nano-modified CSA were also analyzed, advancing its widespread application in rapid repair of special engineering.

Impact of treated sewage water on early strength development of calcium sulfoaluminate cement paste: A comparative study

This study investigates the use of treated sewage water (TSW) as a substitute for fresh tap water (FTW) in concrete production using calcium sulfoaluminate (CSA) cement. The research addresses concerns about freshwater scarcity and emphasizes CSA cement's rapid setting properties, crucial for emergency constructions like military airfield recovery. The focus is on the early-age properties of CSA paste mixed with TSW, with assessments conducted at 4 hours, 1 day, and 3 days post-mixing. Key parameters, including slump, setting times, and hardened characteristics, were evaluated. TSW contained significant metal concentrations and a high pH, with total dissolved solids exceeding FTW by 67%, yet all parameters remained within acceptable limits. Analytical techniques identified ettringite (AFt) as a primary hydration product, while ye'elimite (C4A3Š) was present as a component of the unhydrated clinker in the CSA cement. Simulations showed improved stability in the TSW-CSA interface compared to FTW, although early hydration was slower, likely due to delayed C4A3Š hydration and increased AFt formation. Initially, CSA/TSW pastes presented a refined microstructure, which altered by 3 days. Despite a 14% faster final setting time, compressive strength was 21% lower at 4 hours. These findings highlight TSW's potential as a sustainable alternative in CSA cement mixing, necessitating further research for long-term performance evaluation.

Evaluation of Material Characteristics and Durability of Mixture of Carbon-Eating Concrete and Electric Arc Furnace Slag via Optimal Carbon Dioxide Curing

This study evaluates the material characteristics and durability of a mixture of carbon-eating concrete (CEC) and electric arc furnace slag. Due to the high C<sub>3</sub>A content present in the electric arc furnace reducing slag binder used in the CEC mix, the initial and final setting times of CEC are observed to be 18.8% and 7.0% faster than those of ordinary Portland cement (OPC), respectively. The optimal carbon dioxide curing condition is determined by varying the pressure and temperature variables within the scope of this study. The 3-day compressive strength of CEC under optimal carbon dioxide curing conditions is observed to exceed the 28-day compressive strength of OPC. The formation of calcium carbonate, which contributes to early strength, is confirmed via scanning electron microscopy and thermogravimetric analysis. Additionally, CEC exhibits significantly higher improvements in abrasion resistivity and chloride-ion penetration resistivity when subjected to carbon dioxide curing compared to OPC.

Performance evaluation and mix design of ambient-cured fly ash-phosphogypsum blended geopolymer paste and mortar

A practical mix design and performance metrics for fly ash-phosphogypsum blended geopolymer paste and mortar is lacking. This study focused on investigating the physico-chemo-mechanical performance and mix design of ambient-cured fly ash-phosphogypsum geopolymer paste (FPGP) and mortar (FPGM). The geopolymer was formed by reacting binary powder precursor (fly ash+phosphogypsum) and alkaline activator (NaOH+Na2SiO3). The fly ash was substituted with varying weight proportions of phosphogypsum (i.e., 10 %, 20 %, 30 %, 40 %, 50 %). Experimental testing and analysis were done based on ASTM standards, XRF, XRD, SEM-EDS, ANOVA, and Python. The workability, setting time, flexural strength, compressive strength, morphology, and mineralogy were studied. The multivariate regression approach was used to model the relationship between compressive strength and alkaline liquid/precursor. The optimum mixture conditions for FPGP and FPGM were 30 wt% phosphogypsum, alkaline liquid/precursor of 0.4, 10 M NaOH, Na2SiO3/NaOH of 1.5, and binder/aggregate of 1.0. The results showed that the workability of FPGP ranged from 185 mm to 112 mm while that of FPGM ranged from 145 mm to 100 mm. The FPGP and FPGM had considerably lower initial and final setting times of (18 – 37 min, 81 – 155 min) and (14 – 29 min, 67 – 142 min), respectively. The compressive strength of FPGP ranged from 7.3 MPa to 27.24 MPa while that of FPGM ranged from 9.5 MPa to 43.27 MPa. There was a strong connection between compressive and flexural strength giving R2 values > 0.8. Based on the adjusted R2 values and ANOVA, the proposed mix design models were statistically significant since the p-value (0.000) was less than the 0.05 significance level and the value of F (197.953) was greater than the critical value of 1. At high curing duration, the concentration of NaOH and alkaline liquid/precursor facilitated the dissolution of Ca2+ in phosphogypsum and Si4+and Al3+ in fly ash forming a C-(N)-A-S-H matrix crucial to the strength development of geopolymers. The statistical metrics implied a good performance accuracy and reliability of the proposed model equations and can find practical applications in construction materials design. For optimal results, it is recommended to use the prediction models within the specific input parameters employed in this study.

Evaluation of setting and hardening properties of accelerator and slag-silica fume-cements

Industrial solid waste is used as a supplementary cementitious material (SCM) to replace cement, promoting the recycling and improving resource and economic sustainability. In this study, an organic combination of SCMs was prepared, along with the preparation of composite cementitious materials (CCM) that can be tailored to the aluminum sulfate alkali-free liquid accelerators. The findings revealed that a combination of 30% SCMs, including 10% slag, 15% silica fume, and 5% treated hardened cement powder (T-HCP), was blended with cement to form a CCM. Under the influence of the accelerator, the initial setting time of CCM is 1 min 20 s and the final setting time of CCM is 3 min. The compressive strength at 1, 3, and 28 days reaches 17.2, 29.9, and 51.6 MPa, respectively. CCM can utilize SiO2 from silica fume and CaCO3 in T-HCP as the nucleus to facilitate the substantial generation of AFt and Ca(OH)2 in the initial stage. It can be seen that the use of SCM together with alkali-free liquid accelerators in shotcrete not only enables the utilization of solid waste but also greatly improves the performance of shotcrete.

Biocidal properties of gypsum stone modified with Reynoutria sachalinensis raw materials

The current stage of the construction industry development implies increased requirements for building materials to maintain and improve global environmental processes. The understanding by ecologists globally of the danger of anthropogenic impact on the global environment has been reflected in the formulation of Sustainable Development Goals (SDGs). Thus, scientists and engineers are turning to safe plant-based raw materials as innovative building materials. Of particular interest for practice is the use of Reynoutria sachalinensis, which may exhibit biocidal properties. The purpose of this study was to obtain a gypsum stone modified with an extract from the green mass of R. sachalinensis, as resistant coating to fouling by microscopic fungi. The results indicated 10% decrease in the required water addition to gypsum paste when using plant extract, a slowdown of the initial and final setting time of the modified gypsum paste samples compared to the control samples by 6 and 7 min, respectively, and a slight decrease in bending and compressive strengths of the samples of 12.5% and 6%. The 100% resistance of the modified samples to fouling by microscopic mould fungi was also revealed.

Fresh and Hardened Properties of Alkali-Activated POFA-GGBFS Pastes Cured in Ambient Temperature – An Initial Mix Design

Weak soils are characterised by their high compressibility and low shear strength, which requires stabilisation to improve their compaction and strength characteristics before being used for construction projects. Recent trends in soil stabilisation show an increased interest in the application of waste-derived geopolymers as low-carbon materials to address the carbon emission problem related to cement production. This paper presents the preliminary findings of using Palm Oil Fuel Ash (POFA) and Ground Granulated Blast Furnace Slag (GGBFS) binary blends as geopolymer precursor materials. These binary waste material blends were activated using alkaline solutions, namely Sodium Hydroxide (NH) and Sodium Silicate (NS), to synthesise geopolymers at ambient temperatures. Three main factors were considered for the optimisation of the geopolymer mix design, as recommended by past research: alkali equivalent (8-11.5%), activator modulus (0-0.7), and slag replacement (fixed at 30%). Alkali equivalent and activator modulus parameters were varied and tested to establish its initial and final setting times, workability and strength properties, while the slag replacement percentage was set at 30%. This study aimed to determine the most influential parameters to produce the geopolymer material with the highest compressive strength and satisfactory setting times and workability. Single-source alkali activators (NH only) used on POFA-GGBFS produced specimens with smaller flow diameters, longer initial and final setting times, and lower compressive strength than specimens activated with NH and NS. Geopolymer specimens synthesised with NH and NS produce stiffer compounds possessing higher compressive strength values and explosive-type failure modes due to their higher silica content. At ambient temperatures, TM-Mix 2 (7% alkali equivalent and 0.7 activator modulus) produced the highest compressive strength value of 67.3 MPa at 28 days curing, flow diameter of 227 mm, with the initial and final setting time of 25 minutes and 45 minutes, respectively. Consequently, the results show that the preliminary POFA-GGBFS geopolymer mix design could produce sustainably sourced geopolymer compounds with adequate strength and acceptable setting time and workability. This study is part of a current investigation to further optimise the POFA-GGBFS mix design for the purpose of weak soil stabilisation.

Performance evaluation of high early strength micro-expansion geopolymer grout potentially used for sustainable road infrastructure

This study aimed to develop a high early strength micro-expansion geopolymer grout material derived from recycled concrete and ground granulated blast-furnace slag (GGBS), which can be used to fill the subgrade voids and strengthen weak subgrade. A series of grout materials with varying proportions of recycled concrete were prepared, and their setting time, flowability, and strength characteristics were evaluated. The results indicated that the grout material containing 50 % recycled concrete had a final setting time of 29 min, a flow time of 15.2 s, and a 7-day compressive strength of 40.6 MPa, all of which met the requirements for subgrade grout materials. To further enhance the performance of the grout, the additives including 2 % calcium chloride (CaCl2), 5 % magnesium oxide (MgO), and 5 % united expansive agent (UEA) were used. Results showed that the samples containing 50 % recycled concrete and 2 % CaCl2 exhibited a 26.5 % increase in strength after 100 min of curing, while MgO and UEA reduced shrinkage by 112.5 % and 90.0 %, respectively. Additionally, microstructural analysis using SEM and XRD provided valuable insights into the complex interactions between components and their effects on material integrity. The results demonstrated that the use of CaCl2 accelerated the hydration reaction, enhancing early strength, while the expansion agents MgO and UEA mitigated shrinkage and achieved micro-expansion at low concrete content. This study addresses environmental concerns by incorporating recycled materials, positioning the developed geopolymer grout as a sustainable, high-performance alternative in road construction. Integrating waste-derived components and innovative additives represents a significant step towards advancing sustainable practices in infrastructure development.

Effect of Phosphoric Acid and Soluble Phosphate on the Properties of Magnesium Oxychloride Cement.

This study investigates the effects of phosphoric acid (H3PO4), potassium dihydrogen phosphate (KH2PO4) and sodium dihydrogen phosphate (NaH2PO4) admixtures on the setting time, compressive strength and water resistance of magnesium oxychloride cement (MOC). MOC samples incorporating different admixtures are prepared, and their hydration products and microstructures are studied via X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicate that the addition of H3PO4, KH2PO4 and NaH2PO4 reduces the initial and final setting times and decreases the compressive strength. However, the compressive strength of MOC is higher than 30.00 MPa with the addition of 2.0 wt.% phosphoric acid and its phosphate after 14 days of air curing. The water resistance of modified MOC slurries is significantly improved. The softening coefficient of MOC with 2.0 wt.% H3PO4 is 1.2 after 14 days of water immersion, which is 3.44 times higher than that of the neat MOC. The enhancement in water resistance is attributed to the formation of amorphous gel facilitated by H3PO4, KH2PO4 and NaH2PO4. Furthermore, the improvement in water resistance is manifested as H3PO4 > KH2PO4 > NaH2PO4.

Physical and mechanical properties of special cementitious materials modified by nano-particles

Compared to ordinary Portland cement (OPC), sulphoaluminate/ferroaluminate cement (SAC/FAC) and aluminate cement (CAC) are the most promising repair materials due to their excellent early strengths, but the later strengths of SAC/FAC develop slowly, and the later strengths of CAC are obviously declined. This paper studied the effects of nano-SiO2 and nano-ZnO on the physical properties, mechanical properties and early hydration processes of three special cement-based materials and compared them with OPC-based materials. The strength development and early hydration mechanism were revealed by hydration heat, scanning electron microscopy and X-ray diffraction. The test results showed that with the increasing content of nano-SiO2, the setting time of the four cement pastes was gradually shortened, the fluidity of four fresh mortars was gradually reduced, and their compressive and flexural strengths at all ages were improved to different degrees. Nano-ZnO significantly prolonged the setting time of OPC paste and increased the fluidity of OPC mortar, which had a negative effect on its early compressive and flexural strengths, but enhanced its late strengths. After the addition of 1 % nano-ZnO, the initial and final setting time of OPC were about 12 times and 13.4 times that of ordinary OPC paste, respectively. The effect of incorporating nano-ZnO on the physico-mechanical properties of three special cements was similar to that of nano-SiO2. The strength loss of CAC mortar with two kinds of nanoparticles was greatly reduced. The incorporation of nano-SiO2 and nano-ZnO could promote the hydration process of three special cements, resulting in the denser microstructure and higher crystallinity of hydration products.

Numerical modelling of autogenous shrinkage of rice husk ash blended cement mortar

Addition of rice husk ash (RHA) is an effective internal curing method to mitigate self-desiccation and autogenous shrinkage of hydrating cementitious materials. Although a certain number of experimental researches on this topic have been carried out, a comprehensive study about numerical simulation of mitigating effect of RHA on autogenous shrinkage of cementitious materials is still scarce. In this study, a numerical model of autogenous shrinkage of rice husk ash blended cement mortar was proposed. The proposed numerical model was based on Pickett model and improved by taking visco-elastic behaviour of rice husk ash blended cementitious materials into account. Final setting time, chemically bound water, compressive strength, internal relative humidity (RH) and autogenous shrinkage of pure Portland cementitious materials and rice husk ash blended cementitious materials were experimentally studied. Liquid absorption capacity and water vapour desorption isotherm of rice husk ash were also measured. The comparison between the simulated and measured autogenous shrinkage showed that the autogenous shrinkage of rice husk ash blended cement mortar can be predicted accurately with the proposed numerical model.

The Effects of Metakaolin on the Properties of Magnesium Sulphoaluminate Cement.

Magnesium sulphoaluminate (MSA) cement has good bonding properties and is suitable as an inorganic adhesive for repairing materials in civil engineering. However, there are still some problems with its use, such as its insufficient 1 day (d) strength and poor volumetric stability. This paper aims to investigate the influences of metakaolin (MK) on the physical and mechanical properties of magnesium sulphoaluminate (MSA) cement. The hydration products and microstructures of typical MSA cement samples were also analysed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The results showed that the addition of metakaolin reduces the fluidity and shortens the setting time of the MSA cement. The initial setting time and final setting time shortened maximally by 15-27 min and 25-48 min, respectively, with the addition of 10-30% metakaolin. Moreover, the compressive strength and flexural strength of the MSA cement improved significantly with the addition of 10-30% metakaolin at a curing age of 1 d. Compared with the compressive and flexural strengths of the control sample at 1 d, the compressive strengths of the modified samples showed obvious increases of 98%, 101%, and 109%, and the flexural strengths increased by 39%, 31%, and 26%, respectively, although they decreased slightly when the curing ages were 7 d, 14 d, and 28 d. The addition of 10% metakaolin improved the water resistance of the MSA cement immersed in water for 7 d and resulted in even higher water resistance at 28 d. The addition of 10-30% metakaolin improved the volumetric stability of the MSA cement with increasing dosages before 28 d of ageing. XRD and SEM-EDS analyses showed that the metakaolin accelerated the early hydration reaction and optimised the phase composition of the MSA cement. The results indicate that the addition of 10-20% metakaolin improved the strength after 1 d of ageing, water resistance, and volumetric stability of the MSA cement, providing theoretical support for the application of MAS cement as an inorganic bonding agent for repairing materials.

Alteration of cement rheological properties and setting-hardening: Novel insight into the impact of polyaluminum sulfate

The accelerator significantly influences the setting and hardening performance of shotcrete, in order to develop novel setting components, this study investigates the underlying mechanisms through which polyaluminum sulfate (PAS) facilitates the setting of cement paste. QXRD, Isothermal calorimetry, Zeta potential and Rheological test were employed to analyze the effects of PAS addition on the setting and hardening behavior, hydration kinetics, and rheological properties of cement paste. When the dosage of PAS is 10 %, the initial and final setting times are reduced by 54.39 % and 38.57 % respectively, meanwhile the compressive strength after 6 hours increases by 659.09 %. The influence of PAS on cement setting acceleration and rheological properties were analyzed using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and the Water Film Thickness (WFT) theory. PAS leads to an acceleration in particle aggregation rate and an increase in shear stress and plastic viscosity of the cement paste. Furthermore, the accelerated hydration effect of PAS promotes the formation of additional hydration products, strengthens the interparticle connectivity, and facilitates the formation of a rigid network. This study highlights a novel pathway for understanding the rapid setting mechanism of aluminum-based accelerators.

The Effects of Sodium Silicate and Sodium Citrated on the Properties and Structure of Alkali-Activated Foamed Concrete

Alkali-activated slag cementitious (AASC) foamed concrete (FC) has presented challenges such as rapid setting time and poor working performance. The use of sodium citrate (Na3Cit) as a retarding agent can improve the workability and microstructure of AASC foamed concrete. The effects of the dosage, modulus of water glass (WG, the main component is Na2O·nSiO2), and retarding agent on the properties and structure of FC were studied in this paper. The results indicated that using a water binder ratio of 0.4, WG with a modulus of 1.2, and an additional amount of 15% and 0.5% of Na3Cit, the prepared FC had a flowability of 190 mm. Its initial and final setting times were 3.7 h and 35.3 h. Its 7 d and 28 d compressive strengths reached 1.1 MPa and 1.5 MPa, respectively. After hardening, the pore walls were dense and consistent in size, with few larger pores and nearly spherical shapes. The addition of Na3Cit resulted in the formation of calcium citrate, which adsorbed onto the slag surface. This hindered the initial dissolution of the slag, reduced the number of hydration products produced, and decreased the early strength. With increasing curing time, the slag in the FC mixture dissolved further. This led to the decomposition of a portion of calcium citrate and the release of Ca2+. The Ca2+ reacted with [Si(OH)4]4− and [Al(OH)4]−, creating more C-(A)-S-H gel. This gel filled the voids in the FC and repaired any defects on the pore walls. Ultimately, this process increased the compressive strength of the FC in the later stages.

Study on the improvement of grouting stone properties in coal mine goafs using combined denitrifying bacteria.

Grouting can effectively reduce residual deformation of coal mine goafs, but fly ash grouting materials suffer from poor flowability and slow early strength development. Microbially -induced calcite precipitation (MICP), with its high environmental compatibility and minimal disturbance to geotechnical bodies, effectively improves the injectability of grouting slurry in goafs. This study combined Castellaniella denitrificans and Sporosarcina pasteurii to induce calcite precipitation, preparing cement-fly ash slurry with varying water-solid ratios, solid ratios and denitrifying bacteria concentrations. The physical properties of the slurry and the mechanical properties of the grouted stone bodies under sealed curing conditions were measured. Results show that the dual-bacteria MICP improves stone body performance by enhancing cohesive, frictional and interlocking forces, so that the strength of the stone bodies cured by MICP increased rapidly within 7 days, and the strength reached the standard 2.03 MPa at 28 days under conditions of low solid ratio and high water-solid ratio, with the best compressive strength at a denitrifying bacteria concentration with an optical density of 0.8 at 600 nm wavelength. At a water-solid ratio of 1 : 1.2 and a solid ratio of 15%, initial and final setting times were 67.2 and 96 h, respectively, which prolonged the initial setting time and final setting time by nearly 70% and 110% compared with that of the slurry without MICP treatment, indicating that MICP enhances slurry fluidity, providing more time for grouting construction in goafs.

Evaluating the operational properties of concrete admixtures containing molecularly modified polycarboxylate superplasticizers

The objective of this study focused on the design and preparation of a molecularly modified polycarboxylate superplasticizer to develop concretes with enhanced engineering features. For this purpose, polyethylene glycol was chemically modified with maleic anhydride to give the mono polyethylene glycol maleate (MPEGM). Then, polycarboxylate superplasticizer comprising of isoprenyl oxy polyethylene glycol (TPEG) and acrylic acid (AA, PCE-1), and the synthesized MPEGM with TPEG and AA (PCE-2) were prepared through solution radical polymerization. Subsequently, concrete mixtures with different dosages (0, 0.1, 0.15, 0.2, 0.25, 0.3 wt%) of PCE-1 and PCE-2 were prepared. Chemical structure of the synthesized MPEGM and superplasticizers together with their copolymer composition were identified by FTIR and 1HNMR analyses. The molecular weights (Mw) and molecular weight distributions (PDI) of PCE-1 (8.74 × 104, 1.36) and PCE-2 (8.74 × 104, 2.19) were studied by GPC analysis, respectively. The zeta potential of cement particles (2.8 mV) becomes negative in the presence of 0.6 g/L of PCE-1 (− 7.8) and PCE-2 (− 9.5). This implies that electrostatic and steric hindrance forces of adsorbed superplasticizers synergistically provide a situation for appropriate dispersion of cement particles. The results of water-reducing percentage, fluidity, air content, bleeding water rate, initial and final setting times, wet density, flexural and compressive properties, and ultrasonic pulse velocity analyses exhibit significant enhancement on the features of concrete mixtures made of polycarboxylate superplasticizer. The superiority of PCE-2 to PCE-1 was connected to its adsorption-dispersibility potent induced by stronger electrostatic and steric repulsion forces, which result in quality and continuity enhancement in concretes.

Effects of different activators on autogenous shrinkage of alkali-activated slag cement

Despite the exceptional early strength of sodium silicate or sodium hydroxide-activated slags, much emphasis has always been drawn to the volume instability brought on by their autogenous shrinkage. In this study, a ternary composite activation system was developed by introducing sodium sulfate (Na2SO4), and the effect of Na2SO4-Na2O·1.5SiO2-NaOH ternary composite activators system on the autogenous shrinkage, setting time, and mechanical properties of alkali-activated slag (AAS) was investigated. The effect mechanism of different activator compositions on the autogenous shrinkage of AAS was discussed through the internal relative humidity (IRH), surface tension of pore solution, and microstructure analysis. According to experimental results, the surface tension of pore solution can be reduced and IRH increased by increasing Na2SO4 content in AAS. Additionally, the formation of crystals (anhydrite, ettringite, and thenardite) with specific expansion properties can effectively mitigate autogenous shrinkage in AAS with Na2SO4. The proportions of Na2O·1.5SiO2 and NaOH determine the extent to which Na2SO4 impact the autogenous shrinkage of AAS. An optimal composite activator composition for AAS was determined using a model analysis: When the content of Na2O·1.5SiO2 ranged from 5 % to 17 %, Na2SO4 content ranged from 40 % to 55 %, and NaOH content ranged from 33 % to 56 %, the AAS mortar exhibited a compressive strength exceeding 42.5 MPa at 28 days. Furthermore, the autogenous shrinkage strain of AAS paste remained below 1500 microstrain within 7 days, with an initial setting time surpassing 45 min and a final setting time under 390 min.

Design and evaluation of alkali-activated slag-calcined coal gangue cement and the shrinkage control by calcium carbonate whisker

The rapid solidification and significant shrinkage of alkali-activated slag cement are key issues that restrict its practical engineering application. This paper explores the composition design of alkali-activated cements (AAC) with slow coagulation and shrinkage reduction. This paper adjusts the proportion of slag (SG) and calcined coal gangue powder (CCGP), regulates the content of Na2O·2.4SiO2-NaOH-Na2CO3 ternary activator components, and uses calcium carbonate whiskers (CW) instead of SG to prepare AAC with slow coagulation and shrinkage reduction. When the activator is composed of (66 %) Na2O·2.4 SiO2-(2 %) NaOH-(32 %) Na2CO3 mixed composition, the CO32- and Ca2+ in the system react preferentially to produce CaCO3. The decrease of Ca2+ concentration delays the formation of C-(A)-S-H, resulting in the initial and final setting time of AAC reaching 334 min and 346 min, respectively. When the CW substitution rate is 3 %, the 28d compressive strength of AAC reaches 102.2 MPa. The 49d drying shrinkage of the AAC is 7020μm/m and the 49d autogenous shrinkage is 2387μm/m. This is attributed to the combined effect of enhancement mechanisms such as whisker bridging, crack deflection, whisker pullout, whisker–matrix coalition pullout and whisker breakage. This study establishes the relationship between the composition and performance of high performance AAC, which is significance for the resource utilization of coal gangue and the practical engineering application of AAC.