Drying Shrinkage Research Articles

Effects of EVA and SAE Emulsions on Hydration and Drying Shrinkage of Calcium Sulfoaluminate Cement Pastes

Effects of EVA and SAE Emulsions on Hydration and Drying Shrinkage of Calcium Sulfoaluminate Cement Pastes

Collaborative pollution and carbon reduction behaviors of carbonated Pb-contaminated soil stabilized with a low-carbon binder derived from waste concrete

Due to the limited hydration capacity, solidification/stabilization (S/S) with waste concrete powder (WCP) has a low strength. Carbonation can reduce carbon dioxide (CO2) emissions and improve strength of lead-contaminated soil, but its mechanism and environmental behaviors are unclear. In light of this, a comprehensive study was conducted on the compressive strength, lead immobilization, conductivity characteristics, and carbonation mechanism of carbonated Pb-contaminated soils stabilized with WCP compared to calcining 600 °C WCP. Results indicated that with carbonation, the compressive strength of the samples was significantly improved at the early stage (1 d), resulting in increased unconfined compressive strength (UCS) by 2.5-5.2 times due to the filling of pores by calcite. It negatively affected the lead immobilization capacity of highly doped (30%) samples, while this effect reversed after 3 d of carbonating due to the reduced alkaline environment. The lead immobilization capacity decreased after 28 d of carbonating due to the cracking of samples and the influence of a lower pH on the solubility of lead-carbonated hydroxide ((PbCO3)2Pb(OH)2). The water evaporation (saturation <16.8%) led to dry shrinkage cracking and decreased UCS of the samples. Based on this finding, a conductivity model was developed for carbonated and cured samples, accurately predicting changes in saturation levels (R2 = 0.98). A relationship between conductivity and UCS or lead immobilization capacity was proposed. This research proposed an innovative method for the reduction of CO2 emission as well as laid down a theoretical basis for the recovery of WCP and lead-contaminated soils through carbonation.

Research on the performance of foamed concrete based on superhydrophobic bulk modification

Foamed concrete is a kind of lightweight insulation material formed by the uniform mixture of foam and cement slurry. The superhydrophobic bulk modification of foamed concrete can reduce its high water absorption and prolong its service life. In this paper, the compatibility of three hydrophobic agents named polydimethylsiloxane (PDMS), isoctyltriethoxysilane (ICTS) and SBT®-TIA with foams was studied, and the reasons of incompatibility were revealed. Then, the superhydrophobic bulk foamed concrete system was constructed by physical foaming method, adding polydimethylsiloxane (PDMS), calcium stearate (CS), nano-silica (NS) and covering the surface of the specimen with 200-mesh wire mesh. The results show that the maximum contact angles of the meshed surface and the internal polished surface of superhydrophobic foamed concrete were 162.7° and 153.5°, respectively. At the same time, the water absorption rate of the modified specimen was significantly reduced, and the reduction rate was up to 90 %. In addition, the deterioration degree of thermal insulation performance after soaking and the dry shrinkage rate were significantly reduced compared with ordinary foamed concrete. Scanning electron microscopy (SEM) revealed that increasing the multi-scale roughness could improve the hydrophobic properties of foamed concrete. Fourier infrared spectroscopy (FT-IR) also confirmed that low surface energy groups such as -CH2 and -CH3 in PDMS bonded to the cement hydration products, indicating the successful preparation of superhydrophobic bulk foamed concrete.

A data-enhanced approach for early-age drying induced moisture transport analysis on in-situ casted textile fibre reinforced concrete

With the addition of textile fibres that alters pore structure, the novel Textile Fibre Reinforced Concrete (TFRC) exhibits great potential in reducing drying shrinkage and enhancing long-term durability. To advance material design, this study aims at developing a coupled experimental-numerical framework with a data-enhanced approach to identify the essential material properties that govern the moisture transportation in TFRC. The scope of analysis covers the TFRC manufactured with various fibre types and different fibre volumes, where the time-dependent effect associated with early age is investigated. An inverse analysis framework, coupling Particle Swarm Optimisation (PSO) and extended support vector regression (XSVR), is developed and validated against experimentation by monitoring moisture distribution. Results reveals that the incorporation of textile fibres leads to a substantial reduction in the moisture diffusivity of TFRC, as opposed to conventional concrete of identical w/b and aggregate content. Notably, TFRC mixtures with 0.4 % Nylon twist and PTT600 fibres showed a 95 % reduction in moisture diffusivity compared to the conventional concrete. This discovery illustrates the capability of textile fibres, when optimally introduced, to mitigate moisture loss from cementitious materials, reducing drying shrinkage of concrete building. The proposed approach is demonstrated to be able to robustly quantify the early-age moisture transportation in TFRC, which is of potential to guide future concrete design of using textile fibre reinforcement towards controlling early-age shrinkage in building industry.

Recycled glass concrete with cementitious materials: Study of mechanical prediction model and dry shrinkage mechanism

Recycled Glass Concrete (RGC) exhibits low mechanical strength due to the loose structure of its interfacial transition zone. Adding supplementary cementitious materials is an effective approach to address the issues of low mechanical performance and durability in RGC. In order to improve the performance of recycled glass concrete, three series of tests were prepared for mechanical testing, drying shrinkage testing and microstructure analysis: single-doped limestone powder (RGC-L), single-doped metakaolin (RGC-M), and limestone-metakaolin mix (RGC-LM). The mechanical results demonstrate that RGC, with the addition of 5 % limestone powder and 5 % metakaolin, exhibits optimal strength improvement. Specifically, compressive strength increased by 23.3 %, splitting tensile strength by 38.1 %, and flexural strength by 7.3 %. Additionally, a mechanical prediction model for RGC was proposed, yielding relational equations for splitting tensile strength (ft), flexural strength (fr), and compressive strength (fc): ft=0.14fc0.93,fr=0.72fc0.56. The drying shrinkage results indicate that RGC containing 10 % limestone powder and 20 % metakaolin exhibits the best performance, with a 32.5 % reduction in shrinkage rate. Microstructural analysis revealed that the reaction between Al₂O₃ in metakaolin and limestone powder produces CO₃-AFm, which results in a denser structure in the interfacial transition zone of the recycled glass concrete. Ultimately, this study elucidates the micro-mechanisms and drying shrinkage mechanisms of limestone powder and metakaolin in RGC, offering a promising approach for the effective utilization of construction waste.

Deformation and mechanical properties of foamed concrete under various components and pore structure

Based on macroscopic experimentation and microcosmic testing techniques, the effects of water-binder ratio, water reducer, fly ash and rubber particle content on the settlement, compressive and folding strength, dried shrinkage rate and microstructure of foamed concrete were investigated. The sample's porosity and average pore diameter were measured and combined with the sample's settlement, mechanical properties and dry shrinkage to analyze the difference of the microstructure and its influence on the macro properties in order to provide a basis for the control of the settlement and dry shrinkage of foamed concrete. The results demonstrated that the optimal water-to-binder ratio enhanced the ability of the froth and cementitious material to disperse, as well as the cementitious material's capacity to uniformly envelop the bubbles. It is evident that the water-reducing agent can enhance the pore structure of foamed concrete because the pore wall structure is more complete. By re-hydration of fly ash with the calcium hydroxide produced by cement hydration, internal cavities can be filled to a greater extent. Rubber powder can reduce the strength and increase the settlement deformation of foamed concrete, but it can effectively limit the concrete's dry shrinkage deformation. The settlement of the earlier slurry will alter the pore structure of the later material, and the pressure will fracture and fuse the internal pores, resulting in smaller porosity and larger mean aperture.

Synergetic effect of multiwalled carbon nanotubes on mechanical and deformation properties of engineered cementitious composites: RSM modelling and optimization

Engineered cementitious composites (ECC) have outstanding energy absorption and ductility, but their primary drawbacks continue to be their poor elastic modulus and severe drying shrinkage. Therefore, the incorporation of multiwalled carbon nanotubes (MWCNTs) to mitigate the stated drawbacks and also the influence of MWCNTs on the mechanical characteristics of ECC has been examined. However, the primary goal of this research investigation is to apply the response surface methodology (RSM) modelling for optimizing multiple objectives, effectively handling variable interactions, and achieving significant improvements. A total of thirteen mixtures were produced through RSM modelling using two input factors including different concentrations of MWCNTs at 0.05 %, 0.065 %, and 0.08 %, as well as varying concentrations of PVA fiber at 1 %, 1.5 %, and 2 %. The central composite design (CCD) technique of RSM modelling was used in the production of these mixtures. The results demonstrated that the incorporation of 0.05 % MWCNTs and 1 to 1.5 % PVA fiber together considerably enhanced all of the characteristics of the ECC. The optimum compressive strength, flexural strength, tensile strength, and modulus of elasticity of the ECC were recorded by 74.28 MPa, 14.14 MPa, 5.51 MPa, and 31.10 GPa at 0.05 % MWCNTs at 28 days correspondingly. Furthermore, the drying shrinkage is getting decreased as the extent of MWCNTs increases in ECC. It has been concluded that the use of 0.05 % of MWCNTs and 1 % to 1.5 % of PVA fiber provided good outcomes for construction purposes.

Implementing linear mixed effects models to enhance estimation of the dimensional stability of wood of Laurus nobilis L.

Aim of study: The properties of wood of laurel (Laurus nobilis L.) have not yet been adequately described. For example, information on variables related to dimensional stability during drying (shrinkage) is lacking, even though this is a key factor determining the suitability of the material for industrial uses with high added value. The aim of this study was to construct models for estimating shrinkage variables by using wood density as the predictor variable. Area of study: Seventeen laurel trees were felled in an inland area of Galicia (north-western Spain) in order to obtain the material for testing and modelling. Material and methods: The experimental tests were performed on 958 small standardised, defect-free wood specimens. Main results: The wood under study was moderately heavy and volumetrically unstable. Density varied only slightly, but volumetric shrinkage varied statistically significantly within and between trees. A linear mixed effects model was constructed to predict the variation in volumetric shrinkage from the oven-dry density, including the factors tree and height in the stem, with random slopes and intercepts. Research highlights: The model proved valid for all sampled individuals up to a height of two metres in the stem, thus enabling estimation of the volumetric shrinkage in commercial basal logs.

Effect of Water to Cement Ratio on Properties of Calcium Sulfoaluminate Cement Mortars

Calcium sulfoaluminate (CSA) cements are a promising alternative to Portland clinker, however, a thorough understanding of their properties is needed for their broader use in the industry. One of the topics that requires a good understanding is the effect of the w/c ratio on the properties of CSA cements. To this end, the aim of this paper was to provide research into the effects of a w/c ratio in the range of 0.45–0.6 on the properties of fresh and hardened CSA pastes and mortars. For fresh mortars, consistency and setting time, as well as plastic shrinkage tests, were conducted, and were complemented by hydration heat tests, carried out on pastes. For hardened mortars, tests of compressive and flexural strength and dry shrinkage, as well as SEM photography, were conducted. It was found that, regardless of a higher hydration rate, the increase in w/c ratio decreased flexural and compressive strength, as well as shrinkage, while increasing consistency, setting time, and hydration heat. Also observed was a significant decrease in strength between 3 and 7 days of curing in mortars with a high w/c ratio. It can be concluded that, regardless of the hydration rate, low w/c ratios in CSA mortars provide better properties than high w/c ratios.

Tailoring high ductility cementitious composite incorporating recycled fine aggregate based on shrinkage and mechanical properties

High ductility cementitious composite (HDCC) is recognized as an ideal structural bonding and repair material due to multiple steady-state cracking and strain-hardening properties. However， higher shrinkage strains and low economic and environmental friendliness limit its wide application. To promote the application of HDCC, recycled high ductility cementitious composite (R-HDCC) was prepared by using recycled fine aggregate (RFA) to replace natural fine aggregate (NFA), and the effects of RFA substitution rate and fly ash content on the mechanical and shrinkage properties of R-HDCC were thoroughly investigated. The results showed that the compressive strength of R-HDCC gradually decreased with the increase of RFA substitution, but its tensile strain was enhanced. R-HDCC, with 100 % RFA substitution, still maintained a tensile strength of 2.66 MPa and a tensile strain capacity of 2.46 %. The high fly ash content improved the matrix ductility, resulting in a 54.19 % increase in tensile strain over natural HDCC. In addition, the incorporation of RFA and fly ash reduced the autogenous shrinkage of R-HDCC due to the internal curing effect, but the total drying shrinkage of the matrix increased with increasing RFA substitution rate. R100-70 showed optimal environmental benefits and engineering application value through environmental impact assessment and economic analysis. Finally, this paper is expected to guide the design of ecological, economical, and high-performance R-HDCC.

Effect of recycled fine powder as a calcium source on fresh and hardened properties of geopolymer mortar

This study explores the efficacy of Recycled Fine Powder (RFP) derived from construction and demolition waste as a sustainable substitute for Ordinary Portland Cement (OPC) as a Calcium (Ca) source in geopolymer mortar. Fresh properties of Geopolymer Mortar (GPM) were evaluated in terms of slump-flow, initial-final setting time, whereas hardened properties were evaluated in terms of Compressive Strength (CS), Water Absorption (WA), porosity, acid attack, and dry shrinkage at both ambient and heat curing. Results indicate that the RFP performs well in all mixes. However, mix C10R10 shows the overall best results, as 17% higher compressive strength was observed as compared to mix C20R0, which further increases to 88% when compared to mix C0R0. Thus, RFP provides sufficient Ca content as an activator in GPM.

An evaluation on the shrinkage deformation characteristics of Chinese yam during multiphase microwave drying based on digital image processing

The deformation characteristics of Chinese yam during multiphase microwave drying (MMD) was evaluated by image processing, and the effects of MMD on the drying characteristics, physical properties, shrinkage behavior, and microstructure of the samples were also investigated. The drying time was significantly reduced by increasing microwave power density. Compared with Scheme I, the time of Scheme V was shortened by 22.22%. The moisture content at the transition point from sublimation to evaporation drying stages (TPS-E) significantly affected the shrinkage of the samples. In Scheme I, the lowest moisture content at TPS-E of 0.354 g. g−1 was found, and the dried products with the shrinkage ratio and bulk density closest to those of FD. The deformation of Chinese yam mainly appeared in the evaporation drying stage. At this stage, the rate of change in cross-sectional area of dried samples ranged from 9.74% to 26.76% for Schemes II to Scheme V, compared to 2.03% for Scheme I. Similarly, the shrinkage ratio of the dried samples in Schemes II, III, IV, and V increased from 16.82% to 21.12% at TPS-E to 29.23% to 51.28% at the end of drying, respectively. Additionally, the shrinkage caused by the pores collapse of the samples because of the high moisture content at TPS-E (Scheme III, IV, and V) during the evaporation drying stage resulted in increases of bulk density. The present study can provide valuable insights for rational control of shrinkage and deformation of fruits and vegetables in MMD. Industrial relevanceChinese yam is a widely used food and medicinal resource in China due to its rich nutritional and medicinal values. Since the moisture content of Chinese yam can reach as high as 70–80%, drying serves as an effective method to broaden its application. However, shrinkage and deformation of materials during drying are common forms of appearance deterioration that can directly impact consumer acceptability. MMD has proven to be a promising drying technology. Nevertheless, improper drying parameter settings may lead to a deterioration of the appearance quality of MMD products. Therefore, comprehending the information of shrinkage and deformation of Chinese yam during MMD and effectively regulating these processes is essential. Mastering these aspects is critical for enhancing the economic value and consumer acceptance of dried Chinese yam products.

Nano-SiO2/polyurethane modified unsaturated polyester resin mortar for thin layer repairing on airport pavement

This paper introduces a novel toughened polymer mortar designed for runway repair, featuring outstanding impact resistance, high strength, and cost-effectiveness. To augment the toughness of unsaturated polyester (UP) polymer mortar, nano-SiO2 and polyurethane (PU) were incorporated. Firstly, the optimal dosages of nano-SiO2 and PU were determined through tensile test and impact test. Then, the modification mechanism of nano-SiO2/PU on UP resin was explored by microscopic image technology. In addition, the compression, flexural, fluidity, flexural bond strength and construction time tests were carried out to determine the optimal formula of nano-SiO2/PU modified UP resin mortar. Finally, the durability, impact resistance, impermeability resistance, skid resistance, and interlayer bond strength of modified UP resin mortar were studied and compared with those of pure UP resin mortar and epoxy (EP) resin mortar. Results show that the optimum proportion by mass for nano-SiO2/polyurethane modified UP resin is, UP resin: PU: dibutyltin dilaurate: nano-SiO2: initiator: accelerator: diluent: plasticizer = 1: 0.1: 0.002: 0.01: 0.01: 0.01:0.15:0.01. Furthermore, the mass proportion of modified UP resin to aggregate is 1: 1.2. In nano-SiO2/PU modification of UP resin, the -NCO groups of PU have been involved in chemical interaction with the -OH group of UP, while nano-SiO2 and UP resin are blended physically only. Compared with pure UP resin mortar, the nano-SiO2/PU modified UP resin mortar exhibited a 44% reduction in shrinkage rate, approximately 20% less corrosion loss, a 32% decrease in freeze-thaw loss, a 37% improvement in impact resistance, and increased shear bonding strength, flexural bonding strength, and tensile bonding strength by 44%, 33%, and 47%, respectively. Although the modified UP resin mortar demonstrated slightly lower performance in terms of dry shrinkage, corrosion resistance, skid resistance, and tensile bond strength compared to EP resin mortar, its freeze-thaw durability, impact resistance, flexural bond strength, and shear bond strength surpassed those of EP resin mortar. All three materials exhibited excellent impermeability. Leveraging the advantages of PU and nano-SiO2, the modified UP resin presents a promising repair material for airport pavement with enhanced toughness, high stability, and reduced cost.

Investigating the use of bamboo charcoal to reduce carbon emissions in geopolymer mortar

This study explored the development of carbon-sequestering building materials by integrating bamboo charcoal into geopolymer mortar (GPM). GPM containing bamboo charcoal was prepared and assessed for their flowability, mechanical properties, drying shrinkage, fine pore structure, and carbon emissions. The findings suggest that while bamboo charcoal diminishes the flowability of GPM, utilizing bamboo charcoal with appropriate particle sizes can yield satisfactory flowability. The particle size and shape of the bamboo charcoal also significantly affect the mechanical properties and drying shrinkage of GPM. Using bamboo charcoal T1 (1 mm) and T#25–80 (0.18–0.71 mm) as fine aggregates resulted in higher strength and lower drying shrinkage rates. The spherical 2 K (1 mm) as fine aggregate improved the compressive strength and inhibited the drying shrinkage of GPM. The incorporation of bamboo charcoal increased the content of pores larger than 2μm in GPM, thereby reducing its compressive strength. Among all sizes of bamboo charcoal, the mid-range particle sizes of T1 and T#25–80 had the minimal impact on the volume of pores larger than 2μm and are most suitable for use as fine aggregates. The use of bamboo charcoal significantly reduced the carbon emissions of GPM. With a 12% incorporation of bamboo charcoal, the carbon emissions of GPM were reduced by 81% compared to cement mortar, and it is predicted that GPM can achieve carbon neutrality when the incorporation rate of bamboo charcoal reaches 20%.

Development of sustainable geopolymer with excavation soil powder as precursor: Cementitious properties and thermal-activated modification

One of the focal and challenging issues in the research on sustainable building materials pertains to the recycling of construction excavation soil. This paper developed the sustainable geopolymer containing waste soil powder (WSP) from the construction excavation soil as a precursor. The WSP contains a large number of inert components, while more active components were generated in 600–1200 °C thermoactivated WSP. Substituting WSP for metakaolin (MK) negatively impacts the alkali-activated polymerization reaction of MK-based geopolymer paste, but the geopolymer paste containing thermal-activated WSP has better micro-properties than the geopolymer paste containing un-treated WSP. Mixing WSP raises the drying shrinkage of geopolymer mortar, while the drying shrinkage is reduced with the addition of 600–800 °C thermal-activated WSP. The maximum drying shrinkage of geopolymer mortar with 75 % 800°C-activated WSP is 36.6 % lower than that of plain geopolymer mortar. Substituting WSP for MK causes a reduction in the strength and permeability resistance of geopolymer mortar. At the constant replacement rate of WSP, the geopolymer mortar containing thermal-activated WSP has better strength and permeability resistance than the geopolymer mortar containing un-treated WSP. At 100 % replacement rate of WSP, the sustainable geopolymer mortar made with 1200 °C thermal-activated WSP still has good compressive strength (36.38 MPa). The waste soil-concrete powder (WSPC) also serves as an alternative precursor for sustainable geopolymer materials. Substituting WSPC for 100 % MK in geopolymer is feasible, and the geopolymer made with 800 °C thermal-activated WSPC is much greater than the geopolymer made with un-treated WSPC. Optimizing WSP/WSPC substitution rate and thermal activation temperature can achieve the sustainable geopolymer materials with good performance.

Development of bio-based lightweight and thermally insulated bricks: Efficient energy performance, thermal comfort, and CO2 emission of residential buildings in hot arid climates

This study explores the viability of using industrial wastewater sludge (IWWS), generated by the mycelium treatment of dyeing wastewater, for the fabrication of lightweight and thermally insulating bricks. The pulverized IWWS was used at various replacement ratios of 0, 5, 10, 15, and 20 wt% of clay. The mixture was subjected to firing temperatures of 700, 800, and 900 °C. The effect of applying IWWS to the brick characteristics is assessed through an examination of the physico-mechanical and thermal properties. The utilization of IWWS resulted in a significant enhancement in apparent porosity (34.4 %), cold water absorption (25.6 %), boiling water absorption (28.5 %), linear drying shrinkage (5.1 %), and linear firing shrinkage (7.9 %) using 20 % IWWS at 900 °C. Furthermore, the density, compressive strength, and thermal conductivity were reduced as the substitution IWWS ratio increased, reaching up to 1662.9 kg/m3, 11.56 MPa, and 0.198 W/m.K., respectively, using 20 wt% IWWS at 900 °C. The effect of fabricated fired bricks (FBs) on the thermal insulation, CO2 emissions, and energy consumption of residential buildings was tested. This is accomplished by using energy modeling tools, such as Honeybee, Ladybug, and Climate Studio (Grasshopper plugins), in addition to Galapagos for optimizing wall design. The suggested wall design is being used in a communal residential building located in two distinct climatic regions, namely Cairo in Egypt and Jazan in Saudi Arabia. According to the projected mean vote (PMV) and anticipated percentage of discontent (PPD) measures, the utilization of fabricated FBs as wall materials exhibits significant improvements in thermal comfort. Furthermore, they lead to a 6 % and 7 % drop in CO2 emissions in Cairo and Jazan cities, respectively, as well as a significant 38.8 % and 39 % reduction in energy consumption in Cairo and Jazan cities, respectively. Therefore, the use of fabricated FBs demonstrates itself as a feasible and environmentally friendly choice for building construction.

Solid waste-based low-carbon autoclaved aerated concrete: Relationship between engineering properties and microstructure

A novel low-carbon autoclaved aerated concrete (AAC) was developed to enhance the high valuable use of solid waste in production, incorporating furnace slag, metro shield sand, and quartz tailings sand as 100 % siliceous raw materials, constituting 60 % of the total weight. In this study, comprehensive analyses were conducted on its engineering properties, including density, compressive, flexural, and splitting tensile strengths, and thermal conductivity. Advanced techniques such as X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and high-resolution Industrial CT scanner (X-CT) were employed to examine AAC's material composition, hydration products, and pore structure characteristics at the microscale. The results indicated that the addition of 10 % furnace slag resulted in a specific increase of 5.5 % in compressive strength. However, escalating the furnace slag content to 30 % proved detrimental to the toughness and dry shrinkage of AAC. The microstructure analysis indicates that the use of furnace slag can improve the connectivity and roundness of pores and reduce the probability of large pores (>0.01 mm3), which will reduce the risk of damage localization. Furthermore, furnace slag in AAC enhanced sustainability and cost-effectiveness compared to metro shield sand and quartz tailings sand. Based on the TOPSIS model, an optimal AAC mixture, considering engineering performance, economy, and sustainability, was derived by blending the three types of solid wastes.

Effect of fly ash and gypsum on drying shrinkage and mechanical properties of one‐part alkali‐activated slag mortar

AbstractOne‐part alkali‐activated materials can be processed into semi‐finished products by mixing a solid activator with the powder. They only require the addition of water, which greatly improves their commercial feasibility. So, we used one‐part alkali‐activated slag mortar to investigate the effects of the dosages of the activator (sodium metasilicate), fly ash (FA), and gypsum on its fluidity, flexural strength, compressive strength, and drying shrinkage. The microscopic mechanisms of the mortar were analyzed using scanning electron microscopy and x‐ray diffraction. The below conclusions were drawn. First, the drying shrinkage and compressive strength of the mortar gradually increased with the increase of the activator dosage. Second, the drying shrinkage of the mortar initially decreased and then increased as increasing FA substitution, while the compressive strength decreased gradually in the early stage and then increased and decreased in the later stage. Lastly, by increasing the gypsum dosage, the drying shrinkage of the mortar was significantly reduced. However, the compressive strength gradually decreased. Besides, when adding 20% of FA and 2.4% of gypsum, it was found that ettringite, which underwent expansion, formed in the system. This not only reduced the drying shrinkage by 25.3% but also increased the compressive strength by 1.3%. Furthermore, our investigation has led to the development of a low‐shrinkage one‐part alkali‐activated slag and FA mortar, which not only facilitates the recycling of solid waste materials but also presents commendable environmental and economic advantages.

Preparation and Performance of Cement-Stabilized Base External Curing Agent in a Desert Environment

To explore and deal with the difficulty in curing cement-stabilized bases in desert environments, curing agents were prepared to enhance the curing effect on the base in this research. The composite curing agent was prepared through orthogonal experiments and the durability of the curing agent coating were studied by simulating a desert environment. Subsequently, the curing effect on the performance of bases was analyzed. Finally, the hydration degree of cement was studied via scanning electron microscope (SEM), thermogravimetric analysis (TG), and X-ray diffraction analysis (XRD), and the curing mechanism of the curing agent was explored. The results show that the composite (paraffin emulsion is the main component of the film, vinyl acetate-ethylene copolymer dosage is 20%, ethanol ester-12 dosage is 10%, and sodium silicate dosage is 18%) could effectively improve the water-retention performance (water-loss ratio: 2.36%) and mechanical properties of the specimen (7 d compressive strength: 7.48 MPa; 7 d indirect tensile strength: 0.70 MPa). The dry shrinkage coefficient of the specimen with composite curing agent was reduced by 116.26% at 28 days. The compressive strength of dry and wet freeze could reach 7.48 MPa and 6.88 MPa, respectively. The durability of the curing agent-coated base met the requirements of pavement performance in desert areas. The results of XRD, TG, and SEM indicated that the curing agent promoted hydration. In addition, the number of C-S-H gel and AFt crystals significantly increased. The curing difficulty of road bases in desert areas could be reduced effectively through the application presented in this study, which contributes to the conservation of natural and human resources.

Long-Term Drying Shrinkage Strain of Engineered Cementitious Composite Concrete Contains Polymeric Fibers

The lack of concrete tensile stress endurance led to the invention of engineered cementitious composite. However, the absence of gravel from the mixture in addition to the high binder content may lead to high shrinkage strain. Therefore, a radical solution to this problem is worth to be anticipated. The importance of this research lies in investigating the long-term drying shrinkage strain of the engineered cementitious composite since there is a lack of information regarding this behavior. Mixes of 30 and 60 MPa strengths were produced with polyvinyl alcohol fibers PVA-ECC and polypropylene fibers PP-ECC. The drying shrinkage strain of PVA-ECC mixes has been compared to PP-ECC mixes for both short term (0–28 days) and long term (0–360 days). Results indicated that all PVA-ECC mixes exhibited lower drying shrinkage strains than PP-ECC mixes. The ultimate drying shrinkage strain was recorded to be 1200 microstrain at 28 days. The increment in drying shrinkage strain after 28 days was 5.6% in PVA-ECC mixes when compared to that in PP-ECC mixes which was 6.77%. For high strength levels, the drying shrinkage strain at the age of 360 days declared a reduction of 3.5% for PVA-ECC compared to PP-ECC mixes. Also, it was lower for mixes with 60 MPa (6.3%) than for mixes with 30 MPa (7.6%). Therefore, despite the higher cement content for mixes with 60 MPa strength, the higher fiber volume fraction and the higher PVA solution percentage restricted the drying shrinkage strain increment. The research also addresses some mechanical tests of engineered cementitious composite concrete such as compressive strength, flexural strength, and strain capacity that may provide a strong relation to the drying shrinkage behavior of the different mixes. The scanning electron microscope images were involved in this research to declare the impact of fiber types on the microstructure of the ECC mixes.