Limestone Sand Research Articles

Plastic waste in dense asphalt mixes for road pavements

Recycling plastic waste in asphalt pavements records increasing statistic figures of application during the last decade worldwide. Due to environmental constraints, but also, to some beneficial properties of plastic waste, recycling in asphalt tends to become current practice, in several countries. In the Aristotle University of Thessaloniki (AUTH), the first attempt to produce asphalt mix using plastic waste consisted of mixing recycled plastic flakes with non-modified binder. Following an asphalt mix design in the laboratory, the whole mass of conventional aggregates was replaced by PET flakes. Recycled PET flakes were chosen to be introduced in the asphalt mix since they are hard, resilient and water repellent. Bitumen emulsion was first preferred as a binder to produce a cold asphalt mix. At a second stage of experimental research, plastic flakes replaced a part of the limestone sand while conventional asphalt 50/70 was used as a binder. At this stage, the experimental research provided more encouraging outcomes. Stability of asphalt mixes decreases as the plastics content in the mix increases, but all recorded values were still within limits of acceptance. At a third stage of research, LDPE recycled material of fine gradation was used to replace a part of the asphalt binder in dense mixes. The objective was to produce a modified binder and a more durable asphalt structure. Test results showed a significant improvement of the performance of asphalt mixes, in terms of strength and deformability of the asphalt mix structure. The research is completed by comparing the conventional techniques with the outcomes of the recycling process and by delineating potential fields of application of the recycled plastics in asphalt pavements.

Use of Milled Acanthocardia tuberculate Seashell as Fine Aggregate in Self-Compacting Mortars.

This study focuses on the feasibility of using ground Acanthocardia tuberculate seashells as fine aggregates for self-compacting mortar production. The obtained results show a promising future for coastal industries as their use eliminates waste products and improves the durability of these materials. The use of Acanthocardia tuberculate recycled aggregate, in terms of durability, improves the performance of all mixes made with seashells compared to those made with natural sand, although it decreases workability and slightly reduces mechanical strength. Proper mix design has beneficial effects, as it improves compressive strength, especially when the powder/sand ratio is 0.7. Three replacement ratios based on the volume (0%, 50%, and 100%) of natural limestone sand with recycled fine aggregate from Acanthocardia tuberculate seashells, and three different dosages modifying the powder/sand ratio (0.6, 0.7, and 0.8), were tested. The fresh-state properties of each self-compacting mixture were evaluated based on workability. The mineralogical phases of the hardened mixtures were characterised using X-ray diffraction, thermogravimetry, and differential analyses. Subsequently, the mechanical and durability properties were evaluated based on the compressive and flexural strengths, dry bulk density, accessible porosity for water and water absorption, drying shrinkage, mercury intrusion porosimetry, and water absorption by capillarity. Therefore, the use of Acanthocardia tuberculate seashells in cement-based systems contributes to circular economy.

Performance of Ore Sand as Aggregate for Interlocking Blocks

The search for alternatives that can replace conventional materials extracted from nature is crucial for environmental sustainability. This is especially the case for construction and geotechnical engineering, as this sector is a major consumer of the planet’s natural resources. This paper explores the use of ore sand (OS) tailings with fine aggregate characteristics, which are generated during exploration of iron ore and usually stored in stacks, in terms of their potential for replacing conventional aggregates (gravel, natural sand, and limestone sand) used in interlocking paving blocks for light-traffic pavement. A comparative life cycle assessment (LCA, cradle-to-gate) approach was applied for aggregates in interlocking blocks produced using OS compared to blocks produced with conventional aggregates. The OS was able to replace 24wt% of conventional aggregates (100% limestone sand and 13.3% natural sand), while maintaining compressive-strength performance similar to that of the conventional block (35 MPa). For all eleven environmental-impact categories evaluated in the LCA, the block with OS has improved environmental performance compared to the conventional block. Through the creation and use of a scoring indicator (SI), it was possible to determine that the transport distance of the OS is a limiting factor for the environmental efficiency of the alternative block. Nonetheless, the incorporation of OS mitigates the impacts of block production on eutrophication, acidification, fresh water, human toxicity, and abiotic depletion. The use of tailings reduces the demand for natural resources, decreasing the environmental impact of production and promoting sustainable construction practices.

Utilization of solid waste from tunnel excavation as manufactured sand with different lithology and pre-washing process for preparation of eco-friendly ultra-high performance concretes: Properties and microstructural analysis

Although manufactured sand is becoming increasingly popular to prepare the cleaner and sustainable construction production in face of the depletion of natural river sand, it needs to be further promoted in some advanced concretes like ultra-high performance concrete (UHPC). Different lithological manufactured sands with the same particle gradation were used as fine aggregates to prepare UHPC in this study. Meanwhile, the UHPC mixtures prepared with washed or unwashed sands were also compared. The following aspects were evaluated: flowability, rheology, setting time, mechanical strength, volume stability, thermogravimetric behavior, pore distribution, microstructure characteristics, environmental and economical benefits. Results indicated that sand washing process greatly lowered the apparent viscosity and yield stress, and improved the flowability of UHPC. Increments of 16.7 %, 19.6 % and 15.7 % in flowability were observed for washed granite, tuff and limestone sand UHPC. Pre-washing process significantly delayed the setting times. Tuff sand UHPC demonstrated the optimal mechanical properties (compressive, flexural and tensile strengths), with a compressive strength exceeding 150 MPa at 28 days. In most cases, sand washing process had a slightly beneficial effect on mechanical strengths. The use of washed sand reduced the autogenous shrinkage of UHPC by 5.1%–10.6 %. Tuff sand UHPC possessed the largest cumulative pore volume, while limestone one had the fewest macropores (>100 nm). The cumulative pore volume and total porosity decreased with the addition of washed sands. Compared with traditional UHPC, the utilization of manufactured sand with different lithology and pre-washing process in UHPC could not only illustrate good workability and mechanical strengths, it also demonstrated lower carbon emissions and production costs. The prepared eco-friendly UHPC in this study effectively utilized the solid waste and lessened the environmental burden, which proposed an emerging approach for the application of manufactured sands in green advanced concretes in future work.

Using Tuff and Limestone Sand to Minimize Water Consumption of Pavement Construction in Arid Regions

Abstract Soil compaction is a significant parameter for road construction projects. Since materials and soil compaction play important roles in the stability and durability of roads. This study focuses on the importance of the problems related to water resources in arid regions, considering both the economy and the population in these areas. For this reason, the local materials in Bechar (Algeria) were used to enhance the road construction process. Hence, using the combination of tuff and limestone sand (LS) materials to minimize the amount of water for the road construction compaction is investigated. Different combinations, including 100% tuff, 80% tuff and 20% limestone sand, 70% tuff and 30% limestone sand, and 60% tuff and 40% limestone sand, were evaluated with the Proctor and California Bearing Ratio (CBR) tests. The test results showed that using 60% tuff and 40% limestone sand resulted in the minimum water content of 10.5% compared to other combinations of tuff and limestone sand of this study, and it will be beneficial in arid regions where there is a water shortage. Three different percentages of lime (1%,2%, and 3%) were also added to the optimum mixture. However, the results showed that adding this material has no significant mechanical effects.

Removal of thallium by MnOx coated limestone sand filter through regeneration of KMnO4: Combination of physiochemical and biochemical actions

Treatment of industrial thallium(Tl)-containing wastewater is crucial for mitigating environmental risks and health threats associated with this toxic metal. The incorporation of Mn oxides (MnOx) into the filtration system is a promising solution for efficient Tl(I) removal. However, further research is needed to elucidate the underlying mechanism behind MnOx-enhanced filtration and the rules of its stable operation. In this study, limestone, a cost-effective material, was selected as the filter media. Raw water with Mn(II), Tl(I), and other pollutants was prepared after a thorough investigation of actual industrial wastewater conditions. KMnO4 was added to induce the formation of MnO2 on limestone surfaces, while long-term operation led to enrichment of manganese oxidizing microorganisms (MnOM). Results revealed a dual mechanism. Firstly, most Mn(II) were oxidized by KMnO4 to form MnO2 attaching to limestone sands, and both Tl(I) and residual Mn(II) were adsorbed onto the newly formed MnO2. Subsequently, enzymes secreted by MnOM facilitated oxidation of remaining Mn(II), resulting in the generation of biogenic manganese oxides (BioMnOx) with numerous vacancies during long-term operation. The generated BioMnOx not only adsorbed Mn(II) and Tl(I) but also promoted their oxidation process. This approach offers an effective and sustainable method for removing both Mn(II) and Tl(I) from industrial wastewater, thereby addressing the challenges posed by thallium-contaminated effluents.

Shrinkage performance and modelling of concretes incorporating crushed limestone sand with a high content of fillers for pavement slabs

Because of the gradual depletion of gravel and river sand resources and restrictions on quarrying activities to maintain the ecological balance, limestone crushed sand with a high content of limestone fillers is being explored to be used, as an alternative source of supply, in Portland cement concrete (PCC) for rigid pavement. This paper aims to first present mechanical test results carried out on three types of PCC formulated with crushed limestone sand as fine aggregates, devoid of superplasticizers. Since shrinkage cracking is an important problem for rigid pavement, the shrinkage behaviour of these concretes is then experimentally investigated. Furthermore, three existing models (ACI-209, Eurocode2, and triple-sphere models) and a novel-developed model are used to estimate the mixtures’ shrinkage. Results showed that the designed mixtures exhibited normal shrinkage values. The shrinkage modelling revealed that the proposed model well fitted the experimental data. Besides, Eurocode2 and ACI-209 models may be adapted for the case of limestone concretes containing a high content of limestone fillers and then used to accurately estimate their shrinkage strains. However, the triple-sphere model was unsuitable for these concretes and overestimated their ultimate shrinkage since it does not take into account their high filler content. Nevertheless, by adjusting the paste shrinkage expression, the ultimate shrinkage strain values of the tested mixtures were improved.

Engineering properties and sustainability evaluation of crushed low grade magnesite mortars

China is the country in the world with the most abundant magnesite resources. The ever-increasing deposit of low grade magnesite ore derived from the process of magnesium products has occupied a substantial space and caused environmental damages. In this study, crushed low grade magnesite (CLGM) was prepared and then applied in mortar as fine aggregate to partially or entirely replace natural river sand (30%, 60%, and 100%), while 100% limestone sand (LSS) was applied as the reference group. The findings of this study demonstrated a positive correlation between the ratio of CLGM substitution and the improvement of both engineering properties and sustainable potential in the mortar. Compared with the control group at 28 d, the 100% CLGM mortar exhibited improvements of up to 6% in splitting strength, 25.86% in compressive strength, 16% in porosity reduction, 22.22% in impermeability enhancement, 27.52% in resistance to chloride ion penetration, 21.66% in frost resistance (after 150 cycles), and a remarkable 54.8% in anti-abrasion property. Furthermore, the sustainability evaluation assessed its potential societal value, and highlighted its reduced production costs (down 52.28%) and impressive environmental benefits (notable decreases of 28.3% in ozone depletion potential, 33.2% in land use potential, 38.7% in marine ecotoxicity, and 33.9% in fossil resource scarcity). These findings well demonstrated the feasibility of adopting magnesite tailings as a substitute of conventional aggregate within the construction sector along with substantial economic savings and positive environmental ramifications. The successful application of CLGM mortar in cleaner production can further facilitate the sustainable advancement of environment and construction industry.

Characterizing the Sensitivity of Dielectric Response in Reservoirs with Varying Lithology and Fluid Saturation

Summary This research delivers a comprehensive analysis of complex permittivity’s sensitivity—a key parameter in characterizing electromagnetic (EM) wave absorption and penetration dynamics within oil reservoirs—to various reservoir properties including temperature, pressure, mineralogy (limestone, quartz, and clays), and water saturation. Contemporary estimation techniques, primarily grounded in simplistic mixing rule models, often fail to capture the intricacy inherent to heavy oil reservoirs. Thus, this study, buttressed by extensive experimental data, introduces a distinctive, intrinsically multivariable regression model that better delineates the relationships between dielectric properties and reservoir conditions. Our investigation uncovers water saturation as a pivotal factor in the sensitivity of the regression model, largely due to water’s inherently polar nature. We note that the complex permittivity of the sample diminishes with increasing quartz content and decreasing limestone content—despite limestone possessing a higher individual dielectric constant. Moreover, the presence of clays, primarily found within the pore space delineated by the quartz and limestone sand’s grain boundaries, accentuates the expansive sensitivity of the dielectric constant to water volume, overshadowing the polarizability induced by the double-layer effect of water-sensitive clays. The study additionally uncovers temperature-dependent behavior, characterized by an increase in both components of complex permittivity with rising temperatures, particularly for composite materials comprising diverse rock minerals and hydrocarbons. We also explore pressure as a variable and find no discernible impact on complex permittivity due to pressure fluctuations, although samples with high quartz content exhibit dynamic polarization under pressure. Our multivariable regression model, responsive to all identified parameters, offers a more accurate and realistic interpretation of complex permittivity within the reservoir. The model’s validation on assorted unconsolidated and consolidated core samples underpins its reliability, paving the way for its implementation in any model estimating absorption and penetration dynamics within the reservoir. In summation, the results of this study hold significant implications for reservoir simulation. The regressed models can be directly integrated to bridge the gap between numerical simulation and experimentally obtained relationships. These findings offer insights into the behavior of complex permittivity and its sensitivity to various reservoir properties. The regression model developed herein provides a more nuanced approach to estimating complex permittivity in oil reservoirs, enhancing our comprehension of EM wave absorption dynamics, and contributing to the advancement of more efficient and sustainable oil extraction methodologies.

Assembly and Source of the Lithobiontic Microbial Community in Limestone

Due to its unique rock properties (e.g., porous nature, rough texture, and high calcium and magnesium content), limestone exhibits a high degree of bioreceptivity. However, the mechanisms underlying the establishment of limestone lithobiontic microbial communities (LLMCs) and the extent to which their composition is influenced by the surrounding environment remain enigmatic. Herein, after collecting limestone sand samples, we applied various treatments: rain shelter (RS), organic acid (Oa), nutrients (Nut), inorganic acid (Ia), inorganic acid combined with nutrients (Ia+Nut15), and a blank control (CK). Subsequently, we sampled the treatments after a duration of 60 days. In addition, we collected rotted wood, concrete fences, and soil from the surrounding environment as microbial sources, while using treated limestone samples as microbial sinks. This study yields the following findings: (1) Limestone exhibits high bioreceptivity, allowing rapid microbial colonization within 60 days. Furthermore, compared to the surrounding environment, limestone can accommodate a greater diversity of microbial species. (2) The fungal and bacterial community compositions were explained by surrounding sources to the extent of 35.38% and 40.88%, respectively. The order of sources, in terms of contribution, is as follows: unknown sources > soil > rotted wood > concrete fences. (3) Higher concentrations of Ia and Ia+Nut15 treatments facilitate the colonization of fungi from the surrounding environment onto limestone while inhibiting bacterial colonization. (4) The process of establishing LLMCs is primarily driven by stochastic processes. However, Ia and Ia+Nut15 can mediate transitions in the establishment processes of bacterial communities, while Ia is solely responsible for mediating transitions in the establishment process of fungal communities. Our study offers a fresh perspective on the establishment and origins of microbial communities in limestone habitats. We believe that limestone serves as an excellent substrate for microbial colonization and holds immense potential in ecological restoration efforts within degraded karst areas.

The use of fine fractions of waste from stone quarries in Azerbaijan as sand in the preparation of concrete

Relevance. In recent years, the enterprises of the construction industry of the republic are experiencing an acute need for inert materials, especially for fine aggregates. The sand deposits available in Absheron are very insignificant and, moreover, in some cases do not meet the requirements of regulatory documents. As a result, it is necessary to use imported sands, which are also not always of satisfactory quality due to their significant fine grain and high content of clay and silt particles. In addition, the use of imported sands significantly affects the cost of finished products. Therefore, the study of the possibility of using fine fractions of stone quarry waste instead of sand in the preparation of heavy concrete is very timely and of undoubted interest. In the article, the characteristics of the materials used for the preparation of concrete are considered in sufficient detail, the main properties of limestone sand with different content of dust particles are investigated, the influence of the properties of limestone sand on the strength characteristics of concrete and their resistance to various temperature and humidity influences is studied. For the purpose of comparison, samples were simultaneously made using river sand from the Mingechevir deposit. The obtained results show that in concrete on gravel and crushed stone when using limestone sand, in comparison with concrete on natural sand, the consumption of cement per 1m3 of concrete slightly increases. The purpose of the research. The article deals with the problem of using fine fractions of stone quarry waste as sand in the preparation of concrete. Research methodology. A simple technique was used to determine the volume increment upon swelling. The physical and mechanical tests of sand have been conducted, the study of the particle size modulus when mixed with gravel and crushed stone and the ability to increase volume during swelling are shown. Results. The use of cheap local wastes of shell limestones as small and large aggregates of concrete will make it possible to somewhat cover the need of the construction industry of the republic for aggregates, especially for fine aggregates. Conclusions. Limestone sands obtained by sawing the shell limestones of the Apsheron Peninsula are a suitable fine aggregate for the preparation of concrete.

ASR performance of concrete at external alkali supply – effects of aggregate mixtures and blended cement

ABSTRACT The long-term durability of concrete pavements in wet-freeze climate is influenced by deicing salts used for winter maintenance of roads. Alkaline deicers could also be an external source of alkalis, therefore, their role in respect to the development of deleterious alkali-silica reaction (ASR) should be considered. The performance of mineral aggregate mixtures in concrete was studied using RILEM test procedure ‘60°C concrete test with external alkali supply’. Air-entrained concrete specimens were exposed to cyclic temperature changes, wetting-drying and NaCl solution immersion. Tests revealed the development of concrete expansion in time and associated changes of its elastic modulus for 31 mixtures of fine and coarse aggregate and Portland and fly ash or slag blended cements. The expansive behaviour of air-entrained concrete was strongly influenced by the presence of micro- and cryptocrystalline silica in aggregates. A replacement of nonreactive limestone sand by moderately reactive quartz sand resulted in a substantial enhancement of concrete expansion by a factor of three. The observed reduction of elastic modulus was correlated with more abundant presence of alkali-silica reaction products in concrete. Effects of cement type (CEM I, CEM II/A-V, CEM II/B-S) on the ASR performance of concrete with crushed coarse aggregate and quartz sand are discussed.

The use of waste marble for cleaner production of structural concrete: A comprehensive experimental study

Waste marble is a byproduct that is produced as a result of cutting and reshaping marble stone that is commonly used in the construction sector. From a sustainability perspective, waste marble can be a potential alternative to limestone sand with slightly reduced ecological footprint which is aligned with novel concepts, such as circularity of construction industry. To provide a comprehensive outline of marble’s use as coarse aggregate in concrete production, this study adopted utilizing waste coarse marble aggregate (WCMA) at a quantity of 50% and 100% to substitute coarse limestone aggregates (also natural coarse aggregate (NCA)). Likewise, since marble stone is considered as a metamorphic rock with slightly different microspores, compared to limestone, three different water-to-cement ratios (w/c) of 0.35, 0.42 and 0.49 have also been used. Results show that concretes incorporating WMCA exhibit a slightly better mechanical performance than concretes incorporating NCA, given that the w/c ratio is enough to lubricate WMCA’s surface but not to the point of increasing free water in concrete’s microstructure. In other words, it is found that WMCA is relatively sensitive to the mixture’s w/c ratio which can have a large impact on the resulting physico-mechanical and thermo-durability properties of the specimens. In this regard, despite the WMCA’s slightly enhanced performance in certain thermo-durability tests, the interfacial transition zone (ITZ) areas are found to be more susceptible to deteriorating factors. Nonetheless, the result of this study is found to be significant and point to the suitability of utilizing WMCA as an alternative to NCA.

Influence of Synthetic Limestone Sand on the Frost Resistance of Magnesium Potassium Phosphate Cement Mortar.

Synthetic limestone sand has advantages, such as stable quality and adjustable particle size distribution, and has gradually substituted high-quality natural sand as a fine aggregate in concrete production. The project team has prepared Magnesium Potassium Phosphate Cement (MKPC) mortar by replacing part of the river sand with machine-made limestone sand in equal amounts, which proves that its physical and mechanical properties are obviously better than mortar prepared by whole river sand. However, the research on the impact of machine-made limestone sand on the durability of MKPC mortar has not been carried out. As the repairing material of concrete structures, the frost resistance of MKPC mortar must be evaluated. In this study, the effect of synthetic limestone sand on the frost resistance of Magnesium Potassium Phosphate Cement (MKPC) mortar was investigated by characterizing the strength, mass loss rate, and water absorption of specimens subjected to freeze–thaw cycling. MKPC mortars prepared using solely river sand (M0) or limestone sand (M1) were completely degraded after 225 freezing–thawing cycles in water, whereas the flexural and compressive strengths of MKPC mortar (M2) prepared using both river and synthetic limestone sands was 29.3 and 22.0% of the initial strengths, respectively. The water freeze–thaw resistance of M2 specimens were significantly higher than that of M0 and M1 specimens, and the sulfate freeze–thaw resistance of M1 and M2 were significantly higher than that of M0. The mass loss of MKPC mortar is not more than 0.4% when it is frozen and thawed 225 times in water and 5% Na2SO4 solution, which is far lower than the damage standard of 5%. Based on the favorable composition of the two aggregates, the initial open porosity of M2 was relatively low, owing to the lower water–cement ratio of the mortar at the same flow rate.

New soil abrasion testing method for evaluating the influence of geological parameters of abrasive sandy ground on scraper wear in TBM tunneling

When shield TBM tunneling in abrasive sandy ground, scrapers are loaded with heavy forces resulting from the extrusion and friction processes of sand particles. Scraper wear reflected as displacement or desquamation is related to soil parameters. Due to the lack of reliable test methods, experimental studies on the influence of soil parameters on scraper wear are limited. In the present study, existing soil abrasion testers have been reviewed to discuss the advantages and deficiencies. An improved WHU-SAT soil abrasion tester has been developed to study the influence mechanism of soil parameters on scraper wear. Experimental studies have been conducted to evaluate the variation of scraper wear with quartz content, particle size, particle shape and water content. Two soil abrasion tests have been performed for each case. Scraper wear has been considered to be the average value. The results indicate that scraper wear increases with the increase of quartz content and the growth rate increases. It is related to the particle crushing and adhesion effect of limestone sand. As the average particle size increases, the extrusion and friction between the modeled scraper and the sand particles increases first and then decreases. Thus, scraper wear increases first and then decreases with the increase of average particle size. The trend is generally comparable to the corresponding changes in scraper wear with water content. As quartz balls collide with sand particles and destroy the microscopic friction system composed of scrapers and asperities, scraper wear decreases as the increase of roundness and the falling rate decreases. Optimized solutions such as soil abrasivity evaluation, tunnel alignment optimization and soil discharge improvement have been proposed to alleviate the influence of soil parameters on scraper wear. The present study promotes the rational estimation of sand abrasivity and scraper consumption during the feasibility study of abrasive sandy gournd tunneling using shield TBM.

Performance and durability of self-compacting mortar with recycled sand from crushed brick

The demolition of brick masonry structures and the rejected non-conform bricks are generating a great volume of brick residues. The use of recycled sand from brick residues in the production of mortar could decrease the amount of waste going into landfills and reduce the consumption of natural resources. This paper investigated the feasibility of using recycled sand from crushed brick (RBS) in the self-compacting mortar (SCM). The crushed limestone sand was partially replaced with RBS at different levels (0, 5, 10, 25 and 50%). The properties at fresh state, mechanical behavoir, drying shrinkage and durability of SCM were discussed. As the substitution of limestone sand by RBS increased, the compressive strength of mortars slightly reduced at the age of 28 days (3.3% and 16.9% lower than the reference mortar, respectively for 25% RBS and 50% RBS content); however, which is within the compressive strength requirement in European standard EN 998-2 for masonry mortars. The incorporation of RBS in SCM showed better resistance to chloride diffusion, whereas more attention should be paid to carbonation and sulphate attack. The results indicate that it is possible to manufacture SCM by partially replacing the crushed limestone sand with RBS up to 25% replacement level.

Effect of elevated temperatures on properties of high strength mortars containing ground calcined diatomite with limestone sand

This paper investigates the effect of elevated temperatures on the properties of high strength mortars (HSMs) containing ground calcined diatomite (GCD) produced with limestone sand (LS). In the HSM mixtures at a water-binder ratio of 0.35, GCD is employed in place of cement at replacement ratios of 0, 5, 10, 15 and 20% by weight. The mechanical and microstructural properties of HSMs containing GCD produced with LS are investigated separately at different curing days and elevated temperatures. The results of these properties have indicated that GCD can be employed instead of cement in the HSMs containing GCD produced with LS, and GCD content up to %15 improve the mechanical properties of HSMs. Especially, deteriorations and cracks in the HSMs are seen due to the calcification and expansion of LS used as sand in the mixtures at 1000 °C temperature, and consequently, high decreases in the mechanical properties are observed.

The effect of limestone and bottom ash sand with recycled fine aggregate in foam concrete

To follow resource conservation, the production of optimized and sustainable structures through the use of insulating materials, such as foam concrete, has become a trend in construction industry. Although foam concrete has numerous benefits, the larger use of Portland cement in its mixture and its relatively low thermo-durability properties because of the low quantity of solid materials are of major concerns, challenging its large-scale applications. In that respect, this research evaluates the use of recycled fine concrete aggregate, limestone and bottom ash sand as the main aggregate materials to evaluate the physico-mechanical and thermo-durability properties of foam concrete. To that end, 25 mixes have been produced and a comprehensive series of tests including flowability, compressive and flexural strengths, water absorption, apparent porosity, drying shrinkage, sorptivity, abrasion resistance, thermal conductivity, along with the effect of elevated temperature and its respective cooling regime on foam concretes have been conducted in this study. The results show that foam concretes manufactured with bottom ash and recycled fine aggregates develop a considerably lower thermal conductivity values despite being outperformed in physico-mechanical properties by those mixes produced with limestone sand. Nonetheless, the inclusion of bottom ash sand is found to produce foam concretes with a comparable physico-mechanical and thermo-durability properties to mixes with limestone. The results of this study point to the suitability of utilizing alternative fine-sized aggregates, such as recycled fine aggregates along with bottom ash sand, in the production of foam concrete without compromising the insulating properties of the produced concrete.

Orthogonal Experimental Study on Concrete Properties of Machine-Made Tuff Sand.

Machine-made sand instead of natural sand has become an inevitable choice for the sustainable development of the concrete industry. Orthogonal experiment and grey correlation analysis were used to investigate the performance of machine-made tuff sand concrete. The optimal concrete mix ratio of machine-made sand was obtained by orthogonal test and its working performance was verified. Grey correlation analysis was applied to compare the factors affecting the mechanical properties of the machine-made sand concrete. The test results show that the sand rate has the greatest degree of influence on slump and slump expansion. The mineral admixture has the greatest effect on the 7-day compressive strength of the concrete. Additionally, the water–cement ratio has the greatest influence on the 28-day compressive strength. The mechanical and working properties of the machine-made sand concrete reach the optimum condition when the mineral admixture is 20%, the sand rate is 46%, the stone powder content is 10% and the water–cement ratio is 0.30. Comparing different fine aggregate concretes of similar quality, we conclude that the mechanical and working properties of tuff sand concrete and limestone sand concrete and river sand concrete are similar. The compressive strengths of the mechanism concrete show the greatest correlation with roughness and the least correlation with stone powder content. The stone powder content has almost no effect on the compressive strength of concrete when the stone powder content does not exceed a certain range. The results of the study point out the direction for the quality control of concrete with machine-made sand.

Preparation of Magnesium Ammonium Phosphate Mortar by Manufactured Limestone Sand Using Compound Defoaming Agents for Improved Strength and Impermeability

Magnesium ammonium phosphate cement (MAPC) mortar has recently risen up as high performance rapid repair material for concrete structures. But high costs of the raw materials limit its restoration and maintenance projects on a wide application range. This study proposes the use of manufactured limestone sand with lower cost and wider range of sources in replacement of quartz sand as fine aggregates to produce MAPC mortar. However, the limestone fines of manufactured sand were initially found to have negative effects on the performance of MAPC mortar, causing significant blistering and volume expansion and decreased compressive strength and interfacial bonding strength. To minimize these negative effects, polyether modified silicone (PMS) defoamer and its compound use with mineral admixtures Portland cement and silica fume were investigated on the effectiveness in reducing expansion and improving other properties of MAPC mortar. Results showed that the compound use of PMS defoamer and Portland cement as a new defoaming formula effectively reduced the volume expansion from 7.92% to 0.91%. The compressive strength and interfacial bonding strength were significantly improved by over 34% and 60% respectively. Moreover, this defoaming formula showed improvements in water-tight performance and resistance to chloride penetration. According to the mercury intrusion porosimetry (MIP) analysis, the total porosity of MAPC mortar after defoaming treatment was decreased by about 40% and the pore structure was also modified to be finer by significantly reducing the harmful macropores. Overall, the use of manufactured limestone sands as fine aggregates turned out to be a feasible and economic approach for promoting the filed application of MAPC mortar.