Effects of Aging on the Dry Shrinkage Cracking of Lime Soils with Different Proportions

In this study, the reasonable aging time of lime soils with different ratios was determined to investigate the effect of aging on the internal mechanism of the dry shrinkage cracking of lime soil. To this end, the effects of aging time, lime content, and particle size on the volume crack rate, expansion and shrinkage rate, particle size distribution, and pH were analyzed using a dry–wet cycle, screening, and pH tests. In addition, the changes in the particle structure of the samples and the formation of new substances were analyzed. The results revealed that the volume crack and expansion shrinkage rates of the sample initially decreased, and then stabilized with increasing aging time. In addition, the aging time of the sample increased with increasing lime content and particle size. Further, at the initial aging stage, the volume crack and expansion/shrinkage rates of the sample increased with increasing lime content and particle size. With an increase in the aging time, the pH increased and then decreased significantly to 0.57–1.1% at the reasonable aging time. These indicate that the pH exhibited a significant effect on the reasonable aging time, and this will provide useful insights for the restoration of lime soil sites.

Effects of Steel Fibers (SF) and Ground Granulated Blast Furnace Slag (GGBS) on Recycled Aggregate Concrete

Recycled aggregate is a good option to be used in concrete production as a coarse aggregate that results in environmental benefits as well as sustainable development. However, recycled aggregate causes a reduction in the mechanical and durability performance of concrete. On the other hand, the removal of industrial waste would be considerably decreased if it could be incorporated into concrete production. One of these possibilities is the substitution of the cement by slag, which enhances the concrete poor properties of recycled aggregate concrete as well as provides a decrease in cement consumption, reducing carbon dioxide production, while resolving a waste management challenge. Furthermore, steel fiber was also added to enhance the tensile capacity of recycled aggregate concrete. The main goal of this study was to investigate the characteristics of concrete using ground granulated blast-furnace slag (GGBS) as a binding material on recycled aggregate fibers reinforced concrete (RAFRC). Mechanical performance was assessed through compressive strength and split tensile strength, while durability aspects were studied through water absorption, acid resistance, and dry shrinkage. The results detected from the different experiments depict that, at an optimum dose (40% RCA, 20%GGBS, and 2.0%), compressive and split tensile strength were 39% and 120% more than the reference concrete, respectively. Furthermore, acid resistance at the optimum dose was 36% more than the reference concrete. Furthermore, decreased water absorption and dry shrinkage cracks were observed with the substitution of GGBS into RAFRC.

Study on Strength, Water Stability, Shrinkage, and Microstructure of CFB Slag Modified Cement Stabilized Clay

Circulating fluidized bed slag (CFBS) is an industrial waste produced by coal combustion in power plants. To explore the application of CFB slag in cement-stabilized bases, this paper studies the influence of different dosage of CFBS on the mechanics, water stability, and shrinkage of cement-stabilized soil using laboratory experiments. The hydration activity and interface morphology of CFBS in cement-stabilized clay were observed using XRD and SEM. The improvement mechanism of CFBS on the performance of cement-stabilized clay was revealed. The results indicated that, compared with cement-stabilized clay, cement–CFBS-stabilized clay exhibited better mechanical and water stability, and significantly inhibited the shrinkage deformation of cement-stabilized clay. When the addition of CFBS was 70%, cement–CFBS-stabilized clay had the best mechanics and durability. Microscopic tests show that CFBS contains more active silicon aluminum oxide, which is easily dissolved and the hydration of which produces more gel products, so the mixture structure is denser, the strength is improved, and water does not easily evaporate; it has the characteristics of micro expansion which compensates for dry shrinkage deformation.

The Effect of Adding Fibers on Dry Shrinkage of Geopolymer Concrete

Despite their drastically different chemical ingredients and interactions, geopolymer concrete exhibits many of the same features as ordinary concrete. Among these properties is drying shrinkage. As in normal concrete, dry shrinkage in geopolymer concrete may cause cracking if the geopolymer concrete is bound, which affects the integrity of the structure in the future. It's important to measure drying shrinkage as soon as possible because it's the cause of early age cracking, which happens when the concrete isn't very strong. The purpose of this study is to determine how to reduce the dry shrinkage value of geopolymer concrete by using different types of fibers. Three types of fibers were used to determine their effect on the dry shrinkage of geopolymer concrete when compared with a reference mixture without the fibers. Metakaolin was used as a binder for the concrete geopolymer. As for the fibers, steel, carbon and polypropylene fibers were used in proportions of (0, 0.5, and 1%). The results showed an improvement in dryness shrinkage when adding fibers in general, with a difference in values between the different types of fibers. Steel fibers had the lowest amount of dry shrinkage. The temperature had a direct influence on the decrease in the extent of the shrinking, since the samples handled at higher temperatures had less dryness to begin with. Doi: 10.28991/cej-2021-03091780 Full Text: PDF

Road performance analysis of cement stabilized coal gangue mixture

In order to solve the environmental pollution of coal gangue and the shortage of aggregate resources in road engineering, waste coal gangue is used as road base material instead of natural stone materials. Through physical, mechanical, chemical and activity tests of coal gangue aggregate, the optimal gradation composition of unconfined compressive strength was determined. Through unconfined compressive strength, indirect tensile strength, flexural tensile strength, freeze-thaw and dry shrinkage tests, the influence of cement content on road performance of cement stabilized coal gangue mixture was studied. By means of SEM, ICP AES, XRD and optical digital microscope, the difference between spontaneous combustion coal gangue and Unspontaneous combustion coal gangue was analyzed, the microstructure of cement stabilized coal gangue mixture was characterized, and the strength formation mechanism of mixture was explored. The results show that Spontaneous combustion coal gangue has higher activity than Unspontaneous combustion coal gangue.Based on the selected optimal allocation（BNS:SNS:SSC =71.26:9.41:18.8）,The mixture of 4% cement dosage can not only meet the requirement of early strength 4.16 MPa, but also show an efficient strength growth rate of 36.10%, showing the optimum mechanical properties. The total shrinkage coefficient of cement stabilized coal gangue mixture with 4% cement dosage is 1.12×10-2, which shows that the dry shrinkage resistance is the best. With the increase of time, hydration degree is gradually deepened, and gelled substance is more tightly bonded to aggregates. There is no obvious gap between aggregates, and the integrity of the mixture is enhanced, which can show better road performance. Ca (OH)2, a cement hydration product in cement stabilized coal gangue mixture, takes place pozzolana reaction with active SiO2 and Al2O3 in coal gangue to produce gismondine, which is beneficial to the global strength and the bond quality of the mixture.

IMPROVING THE VOLUMETRIC STABILITY OF WHITE CEMENT BY USING SOME ADDITIVES

This study looked at the effects of three types of additives: limestone powder, Arabian gum AG, and polyvinyl alcohol (PVA), on White Cement Mortar's Physical and Mechanical Properties the mixing ratio for dry shrinkage was 1:2. (Cement: sand) while for other tests, it was 1:2.75 (cement: sand). The limestone powder proportions are (5%, 10%, and 15%) by weight of white cement, while the AG ratios are (0.2, 0.5, and 0.8) % by weight of white cement, the polyvinyl alcohol ratios are (2%, 4%, and 6%). This study was focused at the compressive and flexural strength of the modified mortar, as well as water absorption and drying shrinkage. According to the findings, utilizing of limestone powder as additive in white cement mortar is not advised. Since it had the negative affect on dry shrinkage of the mortar. Furthermore, polymer additives such as AG and PVA significantly increase the reduction of ability of forming crack in white cement mortar. Furthermore, the optimal additive percentages of AG and PVA are 0.5 percent and 6%, respectively.

Enhancing the mechanical and durability properties of fly ash-based geopolymer mortar modified by polyvinyl alcohol fibers and styrene butadiene rubber latex

This study investigated three types of fly ash-based geopolymer mortar (FAG) modified with polyvinyl alcohol fiber (PVA) or styrene butadiene rubber (SBR) latex, where the influence of PVA fibers and SBR latex on the mechanical properties and durability of FAG were studied. The sample performance was subsequently interpreted by characterizing the microstructures of modified FAG samples via the use of scanning electron microscopy (SEM), where the internal structural stress and modification mechanisms were clarified by microstructural analysis. The results showed that the incorporation of PVA fibers mainly promotes the mechanical properties of the samples, especially the early flexural strength, and alleviates their dry shrinkage. However, adding SBR latex to the geopolymer mortar damages the compressive strength and increases the dry shrinkage of samples while improving their freeze-thaw resistance and 28-day flexural strength. The results also show that FAGs have great sulfate resistance. Microstructural analysis reveals that while the dehydrated SBR latex is capable of forming a continuous porous film structure, the fibers also facilitate the formation of a three-dimensional network structure between the dense FAG gels; thus, a more stable geopolymer structure is formed, resulting in an improvement in the toughness and durability of the samples. Furthermore, the SBR latex promotes tight connections between the fibers and geopolymer matrix so that the bond strength between the interfacial transition zone (ITZ) is greatly enhanced.

Product Comparison between Local Product and Technology Aided Mambong Pottery

There are various traditional Malay potteries such as Labu Sayong, Buyung and Terenang. Kelantan traditional pottery known as Mambong. The objectives of this research are to compare and characterize the density, strength, physical appearance and shrinkage of traditional and slip casted Mambong pottery. Traditional Mambong pottery has been brought from the potter at Mambnog village and slip casted Mambong pottery is made by using slip casting method. Density of sample is measured by using Archimedes principal. Traditional Mambong pottery show the higher value of density compared to slip casting Mambong pottery. The average value of density for traditional Mambong pottery was 1.763 g/cm3, while the average value of density for Mambong pottery that was fabricated via slip casting was 1.461 g/cm3. Due to the presence of iron in clay, the colour of Mambong pottery changes from brown to reddish-brown after firing process. Traditional Mambong pottery shows the higher percentage of dry shrinkage which was 9.76 % compared to slip casting Mambong pottery which was 5.72 %. Traditional Mambong pottery also shows the higher percentage of fired shrinkage which was 1 % compared to slip casting Mambong pottery which was 0.58 %. In conclusion, by using slip casting technique, density, physical appearance and shrinkage of pottery can be improved.

Feasibility Evaluation of Replacing River Sand with Copper Tailings

This study aims to realize the resource regeneration application of copper tailing (as fine aggregates for partial replacement of natural fine aggregates), which avoid environmental pollution due to many landfills of copper tailings. The compressive strength and durability (dry shrinkage and sulfate attack) tests were carried out to evaluate the effect of copper tailings replacement on the performance of mortar. The results show that the mortar with copper tailings has higher compressive strength than the one with natural sand. More than 14% improvement in compressive strength can be achieved by adding copper tailings with no more than 40% replacement level. The dry shrinkage of mortar was increased with the copper tailings due to the increase of micro pores in mortar by using copper tailings. Compared with the mortar with natural sand, the dry shrinkage can be reduced by adding copper tailings with no more than 20% replacement level. The sulfate attack resistance is improved by using copper tailings, when the replacement rate is more than 20%. In fact, the micro-aggregate filler effect of copper tailings effectively refines the pore structure and forms more stable, uniform and fine interface micro pores, which is of vital significance for mortar to resist external forces and sulfate ion erosion. However, copper tailings, as a porous material, have water release characteristics in cement mortar. This characteristic is not conducive to the filler effect, which decreases the filling rate in later hydration, leading to higher porosity of copper tailings mortar. More importantly, mortar can solidify heavy metals in copper tailings, which prevents loss of heavy metal such as Cu, Zn, Sr, Zr, As, Ga due to environmental problems.