Gravel Resources Research Articles

Remanufacturing construction and demolition waste and incineration ashes into eco-blocks: Quantitative sustainability assessment

This study performed a sustainability evaluation of a proposed business for remanufacturing concrete materials from construction and demolition waste (CDW) and ash from the combustion of municipal solid waste (MSW) to produce eco-blocks for construction applications. Six possible industrial remanufacturing alternatives are proposed based on commercially available industrial machinery and their economic sustainability was compared by a cost and profit feasibility study. Furthermore, the technical feasibility was evaluated by considering the maturity of the selected machinery based on the relationships among the cost–productivity, power–productivity, and number of workers–productivity pairs. The proposed remanufacturing business achieves a maximum profit of 17,643 USD/day with a minimum remanufacturing cost of 30.65 USD/t for the production of 529 t of eco-blocks in an 8-h factory shift. A quantitative environmental sustainability assessment was performed using the remanufacturing cost, profit, concrete savings, energy savings, CO2 emission savings, and eco-cost savings as criteria based on demographic statistics from the literature for current and predicted CDW and MSW generation. CDW and incineration ash are widely available, so the proposed process is viable worldwide. Based on the technical, economic, and environmental sustainability results, a final sustainability index of 0.874 was calculated, which exceeds literature thresholds for a sustainable business, indicating that the proposed eco-block remanufacturing process has the potential to generate substantial profits, while positively contributing to reducing waste and energy usage by recovering valuable resources and producing value-added products. The remanufactured eco-blocks are prepared in the same way as typical concrete blocks and can be used for all of the same residential, commercial, and industrial construction and landscaping applications. The remanufactured eco-blocks have several advantages over typical concrete blocks, including a much lower manufacturing cost (∼50 % lower), significant environmental and resource savings by avoiding the use of new sand and gravel resources, and improved mechanical properties.

Sulfoaluminate cement-modified loess as bioretention cell filler for nutrient removal from stormwater runoff

In order to reduce the consumption of sand and gravel resources, the use of loess can reduce transportation costs and realize the in-situ construction of spongy in areas with rich loess resources. But the collapsibility and low permeability of loess make it unable to be directly used as the filler of bioretention cells. In this study, sulfoaluminate cement (SAC) mixed with a small amount of basalt fiber was considered to be used for loess modification, and the physicochemical properties and nutrient removal effect of SAC-modified loess as filler in bioretention cells were comprehensively evaluated. The results showed that when the SAC dosage was 15% and the basalt fiber addition was 0% (S15B0) and 0.6% (S15B6) and the curing time was 14 days, the stability and appropriate permeability can be exhibited, which can preliminarily satisfy the requirements of bioretention cell. SAC made the maximum adsorption capacity of S15B0 and S15B6 for ammonia nitrogen (NH4+-N) and phosphate higher than that of sand by 10.96%–31.51% and 45.92%–76.72%, respectively. The hydration products in SAC modified loess can fill the internal pores of loess particles and provide structural support, and ultimately reduce the accumulated pores, mesoporous pore size (20%) and surface homogeneity. Both S15B0 and S15B6 showed good removal effects of NH4+-N and COD. The TP removal efficiency was stable at 95.43%∼99.95%. Both the antecedent drying days and the submerged zone have an effect on the nitrogen removal in the bioretention cells, where a longer antecedent drying days is detrimental to the nitrogen removal, and the installation of a submerged zone improves the nitrogen removal. The basalt fiber can enhance the transformation process from nitrate-nitrogen to nitrite-nitrogen in the bioretention cell. Therefore, the modification of SAC can provide a certain idea for the in-situ use of loess as the filler of the bioretention cell.

Assessment of the properties of interface-modified bamboo aggregates for sustainable concrete construction

To alleviate the serious loss of gravel resources, reduce carbon emissions and improve the sustainability of concrete materials, this study presents an innovative approach to develop a novel eco-friendly bamboo aggregate concrete. The proposed method involves utilizing the abundant and renewable Phyllostachys edulis (Moso) bamboo to create a new type of bamboo aggregate, as a substitute for conventional gravel aggregates. This study modified the bamboo surface using a composite effect of epoxy mortar and polyurethane adhesive to realize the direct application of bamboo aggregates. Compared to unmodified and polyurethane-modified bamboo, epoxy mortar-modified bamboo showed significantly improved physical and mechanical properties. Anti-corrosion properties tests revealed that the modified bamboo, especially epoxy mortar-modified bamboo, was less affected by acidic and alkaline corrosion than the unmodified bamboo and the mass loss rate was almost zero. In the early stages of alkaline corrosion, the strength of the bamboo increased, and then began to decrease after 28 d. The removal of the outer green bamboo significantly improved the adhesion of the adhesive to the bamboo surface, as confirmed by pull-out tests. A sufficient bonding area between the epoxy mortar-modified bamboo and the cement matrix remained after compression damage, whereas obvious debonding behavior between the cement matrix and unmodified and polyurethane-modified bamboo was observed. In summary, epoxy mortar modification significantly improved the comprehensive performance of bamboo aggregates. This study is expected to help improve the utilization rate of bamboo, promote bamboo concrete, and develop sustainable materials.

Electrochemical chlorine evolution reaction to improve the desalination of sea sand

Sea sand, a vital sand and gravel resource, is rich in chloride, which causes corrosion of steel reinforcements. This study investigates the effect of the electrochemical chlorine evolution reaction (CER) on the desalination of sea sand. The results indicate that the chlorine removal efficiency (RE) of sea sand increased from 48.76 to 56.40 % under optimal conditions: a current density of 15 mA/cm2, an electrolysis time of 1 min, and a sodium sulphate-supported electrolyte concentration of 0.05 mol/L. After 30 days of resting, the dissolved chlorine content in sea sand was 0.154 %, which was 21.03 % lower than that of the control group. The electrically active chlorine-mediated desalination process demonstrated excellent dechlorination ability, facilitated the transformation of metal and organic chlorine into liquid and gaseous forms, and reduced the slow release of chloride from sea sand. Therefore, CER is expected to be an efficient method for sea sand desalination.

Quality assessment standards and production technology of artificial sand based on hydraulic concrete construction specifications

Natural sand and gravel resources are a local resource. Natural sand and gravel are non-renewable in a short time and are not suitable for long-distance transportation. After decades of mining, sand and gravel resources in some areas have been exhausted. The transportation distance of natural sand and gravel is getting farther and farther, and accordingly, the price of natural sand and gravel continues to rise. At the same time, continuous and disorderly mining has caused serious damage to the environment and resources. During the construction of large and medium-sized water conservancy and hydropower projects in China, due to the lack of surrounding natural aggregates, most projects use artificial aggregates. In the current national standards for water conservancy projects, the content of artificial sand and gravel powder is clearly defined. Based on the “Hydraulic Concrete Construction Specifications” (SL677-2014), this article summarizes the particle shape, gradation and surface structure of artificial sand, and also calculates the theoretical gradation of artificial sand. To find out the impact of stone powder content on the performance of artificial sand, different levels of stone powder content need to be selected for research and analysis to clarify the impact of artificial sand powder content on concrete properties. Research shows that for concrete made from artificial sand, increasing the aggregate content with a particle size less than 0.075 mm can significantly increase the compressive strength of the concrete. In artificial sand, the content of stone powder will affect the workability, polishability, durability, permeability and water release of concrete. In the artificial sand and gravel production process system, crushing and sand making equipment are the most important sand and gravel production equipment. The research results provide theoretical reference for the application of artificial sand in concrete and the update of artificial sand production technology and equipment.

Experimental study on the basic properties of new biomass bamboo aggregate concrete

Gravel aggregate is an important part of concrete, but the resources of natural aggregate, such as gravel, are increasingly scarce and may have adverse effects on the environment. Therefore, a new biomass bamboo aggregate concrete was proposed in this study, which bamboo aggregate was used to replace gravel aggregate to alleviate the shortage of gravel resources. To study the basic properties of bamboo aggregate concrete and explore its feasibility, tests for compressive strength, splitting tensile strength, flexural strength, and uniaxial compressive stress-strain curve were conducted. The microstructure was also observed. The research parameters included the concrete curing age and different bamboo aggregate volume replacement ratios. The results presented that the mechanical properties of bamboo aggregate concrete were enhanced with increasing age. Compared with the normal concrete, the mechanical properties of bamboo aggregate concrete decreased as the replacement ratio of modified bamboo aggregate increased, but the 28-d compressive strength of modified bamboo aggregate concrete could still reach 74% of that of normal concrete. The mechanical performance of bamboo aggregate concrete was significantly influenced by whether bamboo aggregates were modified. The uniaxial compressive stress-strain model proposed by GB50010-2010 was suitable for bamboo aggregate concrete. The interfacial bonding effect between modified bamboo aggregate and cement matrix was improved.

DFT study on the polyol sacrificial agents for improved clay tolerance of polycarboxylate superplasticizers

With the gradual scarcity of high-quality sand and gravel resources, the increasing mud content in concrete aggregates could strongly adsorb on polycarboxylate superplasticizers (PCE), greatly reducing their working performance. Modifying the molecular structure of PCE or compounding sacrificial agents can effectively improve the tolerance to clay minerals. In this article, using different small molecule polyols and polypropylene glycol (PPG) as examples, density functional theory (DFT) was employed to simulate the adsorption between clay minerals and hydration products. This exploration aims to further understand the anti-clay performance of various sacrificial agents from the perspective of adsorption energy. Ca-montmorillonite (CaMMT) exhibits the lowest adsorption energy among different clay minerals, making it the preferred site for sacrificial agent adsorption. With an increase in hydroxyl number, the adsorption energy between polyol sacrificial agents and montmorillonite decreases. Among polymeric polyols, the adsorption energy between PPG 600 and montmorillonite is the lowest (-10.86 eV), indicating superior anti-clay performance by preferentially occupying active sites on montmorillonite. As the interlayer spacing of montmorillonite increases, the adsorption energy between PPG 600 and montmorillonite initially decreases and then increases, reaching the lowest value at c=15.5 Å. There are more electron transfers (0.858) compared to the electron gain and loss, confirming more interaction between the sacrificial agents and montmorillonite at 15.5Å. This article also provides a crucial theoretical basis for the structural design of anti-clay sacrificial agents, offering insights into addressing compatibility issues between PCEs and clay minerals.

Study on the deterioration characteristics and mechanisms of recycled brick-concrete aggregate concrete under load-freeze-thaw coupling

Using construction waste to prepare recycled concrete is an important way to realize the resource utilization of construction waste and solve the shortage of sand and gravel resources in China. However, the current separation process makes it difficult to completely separate recycled brick aggregate (RBA) and recycled concrete aggregate (RCA), and the cost of high-precision separation is high. Therefore, the mixed-use of RBA and RCA to prepare recycled brick-concrete aggregate concrete (RB-CAC) can effectively reduce the pre-separation cost and has good economic and engineering applicability.In northern China, concrete is often subjected to load-freeze-thaw coupling. However, there are few studies on RB-CAC, and there are fewer studies on its degradation characteristics and degradation mechanism under load-freeze-thaw coupling. Therefore, based on the previous research on the mechanical properties of RB-CAC, RB-CAC was prepared by mixing RBA and RCA in a ratio of 1:1 and replacing natural coarse aggregate (NA) with a replacement rate of 30%. The macroscopic properties and degradation mechanism of RB-CAC under load-freeze-thaw coupling were studied by compressive strength tests, SEM, microhardness tests, and NMR tests. The quantitative relationship between microstructure and compressive strength damage was established, and the deterioration characteristics and mechanism of RB-CAC were explored. The results show that: (1) With the increase in stress ratio, the frost resistance of RB-CAC decreases gradually. Under the stress ratios of 0, 0.2, 0.4, and 0.6, the maximum number of freeze-thaw cycles that can be tolerated is 170 times, 150 times, 130 times, and 60 times (brittle fracture occurs when the stress ratio is 0.6, and freeze-thaws 70 times). After 60 freeze-thaw cycles, compared with 0 stress ratio, the mass loss rate under 0.2, 0.4, and 0.6 stress ratio increased by 0.33%, 0.42%, 1.61%, and the relative dynamic elastic modulus and compressive strength decreased by 4.73%, 2.71%, 14.13%, and 0.25 MPa, 1.07 MPa, 3.58 MPa, respectively. (2) The performance of RCA and the old mortar interface area is better than that of RCA and the new mortar interface area, and the performance of RBA and the new mortar interface area is better than that of RBA and the old mortar interface area. With the increase in stress ratio and freeze-thaw times, the interface thickness of RCA-old mortar is lower than that of RCA-new mortar, the interface thickness of RBA-old mortar is higher than that of RBA-new mortar, the interface hardness of RCA-old mortar is higher than that of RCA-new mortar, and the interface hardness of RBA-old mortar is lower than that of RBA-new mortar. (3) With the increase of the applied stress and the number of freeze-thaw cycles, the effective pore of the specimen shows a gradually decreasing trend, and the invalid pore shows a gradually increasing trend. The total porosity increased by 0.78%, 2.13%, 7.39%, and 0.71%, 2.766%, 3.50%, 4.83%, respectively, indicating that the size of the stress ratio has a greater influence on the porosity than the number of freeze-thaw cycles. (4) The fractal dimension was introduced to characterize the deterioration characteristics of RB-CAC, and the macro-micro relationship was established. The regression coefficients were 0.8784 and 0.9938, respectively. (5) The correlation analysis between the parameters of the multiple interface transition zone and the compressive strength was carried out, and the regression coefficients were all greater than 0.9. The greater the thickness of the interface zone, the smaller the hardness and the lower the compressive strength of the concrete.The research results provide a reference for reducing the separation process requirements of RBA and RCA, reducing the preparation cost of recycled concrete, and further developing high-frost resistance RB-CAC suitable for engineering applications in cold regions.

Damage and Deterioration Mechanism of Coal Gangue Mixed Pumice Aggregate Concrete Under Freeze–Thaw Cycles

The world is facing the problem of depletion of natural sand and gravel resources, and a large amount of coal gangue solid waste is produced in Inner Mongolia, China, which has low utilization rate and causes ecological pollution. In order to improve the gangue in the mining infrastructure construction of a wide range of application prospects, the use of coal gangue as the coarse aggregate of pumice concrete is of great significance. Inner Mongolia is a cold region, and gangue mixed aggregate concrete (MFC) will certainly face the damage caused by freeze–thaw cycles. Therefore, design gangue by different volume replacement rate (0%, 20%, 40%, 60%, 80%,100%) to replace pumice coarse aggregate. The results show that with the increase of gangue substitution rate, the mass loss rate, relative dynamic elastic modulus, and peak stress of MFC decrease, but the trend of peak strain increases. It is mainly attributed to the less Al2O3 and SiO2 content of gangue, which makes the MFC hydration products decrease with the increase of substitution rate and more original microcracks and pores in the specimens. In addition, the damage model of MFC was established by using Weibull statistical distribution theory and the principle of LEMAITRE equivalent effect variation assumption, and the damage evolution characteristics were explored by combining the experimental results. It can provide the theoretical basis for the application of MFC in cold regions.

A model based on the evolutionary game theory for implementing green mining principles in riverine sand and gravel resources

An evolutionary Game Theory (GT) model was presented to study the dynamics between the mine management and government for implementing Green Mining (GM) principles in riverine sand and gravel mines. In this regard, a game was planned in which the mine management is the executing agent, while the government acts as the supervisor. Investigating the performance of the proposed model, regulatory factors such as governmental incentives and penalties were introduced. In order to compare the results, the effects of regulatory measures on strategy changes by mine management were analyzed into two distinct scenarios: classical GT and evolutionary GT, which provide valuable insights into the complex interactions between mine management and government. The Shahed sand and gravel mine near the Kordan River in Alborz province, Iran, was selected as a case study to validate the developed GT models. The results obtained from the classical GT model showed that a fine of $ 0.2 per tonne and a 30% governmental incentive for the mining and equipment costs, may encourage the mine management to choose the GM strategy. Conversely, the results of the evolutionary GT model indicated that by increasing the government subsidy from 30% to 50%, the rate of encouraging the mine management to choose the GM strategy could be accelerated. This situation is similar to the government incentive for mine management in case of fines from $0.2 to $1 per tonne. According to the results of the evolutionary GT model, when the population ratio increases over time, the selected strategy is more compatible and powerful compared to other ones. Therefore, it is concluded that the mine management in Shahed mine may turn to the GM strategy by imposing a penalty more than $0.6 per tonne.

Adapting the ESSENZ Method to Assess the Criticality of Construction Materials: Case Study of Herne, Germany

The steady increase in the world’s population combined with the globally growing need for living space by each individual is leading to an ever-faster consumption of limited resources by the construction industry, particularly sand and gravel. While a consensus exists regarding the sand and gravel resource availability on a global level for long-term supply, it is important to note that local supply shortages may still occur. Thus, this study aims to identify critical aspects of both locally and globally traded construction materials by adapting the ESSENZ method, which evaluates the criticality of globally traded abiotic resources. For the specific case of the local availability of construction materials, a new indicator is introduced: The Surface Squared Driven Indicator (SSDI), which is adapted to the specific conditions of the German market. The modified ESSENZ method is applied in a case study of materials needed for maintaining the material stock of the city of Herne, Germany. The results indicate that raw materials for concrete production in Germany, such as aggregates, are expected to be sufficient in the long term, but silica sand for glass production is only guaranteed for a few decades. Concrete poses the highest supply risk due to its high material demand, with steel and concrete dominating the environmental impacts. Limitations include data availability and the exclusion of certain materials. The adapted ESSENZ method allows for the comparison of criticality results for materials traded globally and locally, offering valuable insights for decision-makers seeking to promote sustainable construction practices.

Use of recycled fine aggregates and recycled powders in sustainable recycled concrete

The shortage of sand and gravel resources has become a global problem. Processing construction and demolition wastes (CDW) into recycled materials and using them to prepare new concrete is conducive to the sustainable development of the construction industry. In terms of recycled coarse aggregate (RCA), relatively mature technical accumulation and industrialization have been formed, but the utilization technology of recycled fine fractions (RF), accounting for more than 40%, is still scarce. In this study, the feasible use of RF, including recycled fine aggregates (RFA) and recycled powders (RP), in recycled concrete was studied from the perspective of fresh properties (empirical and rheological). The results showed that the reduction in the slump was more prominent in Series with RFA than RP. The highest reduction was observed around 31.71% (30% RP) in Series I at 30mins; and 60.98% (50% RFA) in Series II in mix with 50% RFA, which is due to higher friction and higher interlocking behavior due to their rough surface and higher amount of attached mortar. The mix with RP showed the most significant increase in the static viscosity of 271% at 30% RP and 149% with 100% RFA replacement at 30 min of the time interval. Static yield stress increases greater with RP, which may have caused slump expansion to decrease over time. The friction from RFA's rough surface texture and the mix's extra SP and water content enhance dynamic yield stress and decrease viscosity. The study found that the incorporation of RP and FA in the mixes resulted in a noteworthy reduction in carbon emissions compared to the control mix. Specifically, RPC2 and RPC3 exhibited a decrease of 24.35% and 25.00%, respectively. It is also seen that using recycled fines can lead to stable, low-carbon concrete for leading to a sustainable automated construction industry.

Experimental Study on Conventional Recycled Aggregate Concrete Associate with Micro Silica

Abstract: The ongoing need for infrastructure around the world as a result of continued population growth suggests that more aggregate and cement will be needed in the manufacture of concrete. This would eventually result in greater carbon emissions, increased resource extraction, and depletion. The increasing aggregate and cement requirements are a result of the constant global demand for concrete. More extraction occurs as a result, depleting natural gravel resources and increasing CO2 emissions from quarrying operations. Construction costs and carbon emissions could both be reduced by partially substituting recycled material for natural aggregate. Fine aggregate, coarse aggregate, potable water, and the cement-based binder make up the heterogeneous material known as concrete. The heterogeneity is increased more by the presence of coarse particles. An aggregate consumes about 60% to 75% of the overall volume of concrete. The aim of this research work was to develop high performance concrete using recycled coarse aggregate, microsilica, and synthetic macro fibre with the object to boost higher use of recycled coarse aggregate in the construction industry. Concrete is most important material used in the construction industry. Large amount of natural aggregates were used in concrete, this causes the nature. Now a day’s many structures are demolished & rebuilt, demolishing of structures causes problem with dumping of waste material. An important aspect of sustainable construction is recycling or reuse of the construction material and demolition waste. It will maintain a friendly green environment. Recycled aggregates has micro cracks on its surface causes low strength, low workability of concrete. This draw back can be avoided by using micro silica. In this paper experimental results were shown for recycled aggregate incorporating with micro silica.

Shear behaviour of seawater sea-sand coral aggregate concrete beams reinforced with FRP strip stirrups

The preparation of concrete for remote islands or reefs using locally available seawater, sea sand, and coral aggregate can greatly shorten the construction period and mitigate the shortage of river sand and natural gravel resources. This study is the first to experimentally investigate the shear behaviour of seawater sea-sand coral aggregate concrete (SSCAC) beams reinforced with non-corrosive carbon fibre-reinforced polymer (CFRP) strip stirrups. The test parameters included concrete strength, concrete type, and stirrup configuration. The experimental results suggested that CFRP-reinforced SSCAC beams exhibited a brittle shear failure mode because of the sudden CFRP rupture at the bend portions. The ratio of the measured maximum strain to the ultimate tensile strain of the CFRP strip stirrups varied from 36.6% to 47.8%. The critical diagonal shear cracks of SSCAC beams directly penetrated through the coral aggregates and split the aggregates, whereas those in the natural aggregate concrete (NAC) beams bypassed the natural gravel. In this regard, the SSCAC beams exhibited approximately 10% lower shear strength than their NAC counterparts owing to the loss of the aggregate interlocking effect after the occurrence of smooth diagonal shear cracks. The higher the strength grade of SSCAC, the greater the shear strength and service load.

Experimental Analysis and Evaluation of the Compressive Strength of Rubberized Concrete During Freeze–Thaw Cycles

Recycling scrap tires provides an alternative source of fine aggregates for the production of rubberized concrete and this will lead to significant increase in concrete frost resistance, environmental protection, and conservation of natural sand and gravel resources. In this paper, a total of 25 groups of rubberized concrete were produced by adding scrap tire rubber particles of different sizes, contents, and pretreatment methods to replace the fine aggregate, and their compressive strength during freeze–thaw cycles was studied from both the macro- and meso-perspectives. The results indicated that the decrease in concrete strength and weight was notably restricted by the presence of rubber particles during freeze–thaw cycles. The rubber fine aggregate with smaller particle sizes enhanced the concrete frost resistance more significantly, and the F100 of concrete with rubber particles of 1.0–2.0 mm increased from 76.6 to 86.5% by increasing the rubber content from 0.0 to 5.6%. The effects of rubber fine aggregate on concrete compressive strength during freeze–thaw cycles were quantified. On this basis, a forecast model for rubberized concrete compressive strength in freeze–thaw cycles was proposed, and the effects of the particle size, content, and pretreatment of the rubber particles were considered. The calculated results agreed well with the test results both in this study and the relevant peer studies, indicating that the model can provide a good reference for the design and engineering application of rubberized concrete in frigid environments.

Activation and Application of Wet Shotcrete Concrete with Coal Gasification Slag Aggregate

By analyzing the shortcomings of the existing dry shotcrete process in the coal mines and the shortage of natural sand and gravel resources, it is proposed to use coal gasification slag to replace all natural sand and gravel in the preparation of wet shotcrete. Coal gasification slag has alkali-activated cementitious activity, and its strength as an aggregate in cement mortars still shows significant growth after 28d of age. First of all, the gasified slag aggregate cement mortar was mixed with calcium carbide residue to further stimulate its activity, and the effect law of different amounts of calciumcarbide residue on mortar strength was studied. The results showed that the mortar strength increased continuously with the increase of calcium carbide residue admixture, and the mortar strength increased slowly after the admixture reached 8%. With 8% admixture, the flexural strength at 90d age increased by 58.9%, and compressive strength increased by 13.6% compared with 28d age. MIP, XRD and SEM microscopic analyses showed that the incorporation of CCR promoted the alkali-activated cementation reaction of the gasified slag aggregate, eliminated the oriented aggregation of calcium hydroxide at the cement-aggregate interface, improved the interfacial bonding, and significantly reduced the percentage of harmful pores (50-200 nm) and more harmful pores (>200 nm) in the mortar, which explained the microscopic mechanism of the significant increase in mortar strength. Then the mining wet shotcrete was prepared with coal gasification slag as aggregate and calcium carbide residue as cementing material, and the 28d compressive strength reached 34.8MPa, which significantly improved the concrete strength and ensured the stability of the coal mine roadway support.

Spatial and Temporal Changes of Sand Mining in the Yangtze River Basin since the Establishment of the Three Gorges Dam.

The global demand for sand and gravel is at 50 billion tons per year, far exceeding global resource capacities. It reached 7.6 billion tons in 2021 in the Yangtze River Basin (YRB), China. However, production is severely limited in the YRB. Therefore, the incongruity between the supply and demand of river sand is prominent. Wise management of decreasing sand resources in the YRB has become critical since the Three Gorges Dam became operational in 2003. This study synthesized spatial and temporal changes in sand mining activities and quantities along the Yangtze River and its major tributaries from 2004 to 2020. Results from the study show that the mining amount during the period reached 76.2 million tons annually. At the same time, riverine suspended sediment discharge (SSD) downstream of the Three Gorges Dam decreased largely. SSD reduction leads to riverbed erosion, further limiting the riverine sand and gravel sources for mining. Thus, alternative sand and gravel resources, as well as optimizing supply/demand balance, are necessary for sustainable development. There is an urgent need to assess the relationship between river sand resources and exploitation in the YRB for creating a sand and gravel data management system in order to cope with the increasing incongruity between their supply and demand.

Statistical modeling of physical and mechanical responses of roller-compacted sand concrete made with ternary sand using the experimental design method

The rapid development of road infrastructure and the lack of gravel resources have pushed practitioners in the field to develop and propose new alternative materials for road construction. As these novel materials are essentially based on sand, an innovative technique, i.e. the roller-compacted sand concrete (RCSC) technique, has lately been developed. The present paper aims primarily to investigate the effects of the physical characteristics and the mineralogical nature of sand on the mechanical and physical behavior of the RCSC. For this purpose, it was deemed appropriate to choose the design-of-experiment (mixture design) modeling with three factors that are represented by three different types of sand, i.e. calcareous sand (CS), alluvial sand (AS), and desert sand (DS). In addition, it was decided to select the compressive and tensile strength, dynamic modulus of elasticity, and water absorption at 28 days, as responses. Next, a microstructural analysis was carried out using the scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques.

POSSIBILITIES TO REUSE A CERAMIC WASTE AS CONCRETE AGGREGATES

Every year, huge amounts of natural resources are used to produce concrete. Sand and gravel resources are rapidly draining, therefore, it is necessary to reduce consumption. On the other hand, there are a lot of construction waste which can be reused in concrete production. One of possibilities is to use in concrete production ceramic waste. During the research the coarse aggregates were changed to ceramic bricks waste. The changes of fresh concrete workability, density, hardened concrete compression strength, water absorption and frost resistance were evaluated. The results show that ceramic waste has a negative effect to all concrete properties. Ceramic bricks waste should be used to replace coarse aggregate in a lower ratio, such as the possible option of replacing 10 % of coarse aggregates. The stoneware tiles waste show better results (Skominas et al., 2020). This waste can be used replacing up to 60 % concrete coarse aggregates. According to all results can be concluded that stoneware tiles waste is better choice for coarse aggregates production.

Functional and environmental impacts of the use of reclaimed asphalt pavement materials and of foamed asphalt

Environmental safety related to asphalt mixing plants has been a growing concern due to the high temperature of asphalt mixture production resulting in a lot of energy used and much air pollutants released. Asphalt mixtures with foamed bitumen and RAP can reduce this problem. This paper deals with their functional and environmental effects. In the paper, it was introduced that the hot mix asphalt mixtures bound by foamed bitumen and containing RAP materials provides a good workability, in comparison to “traditional” hot mix asphalt mixtures. However, producing foamed bitumen needs special technological steps before using it as asphalt binder. The use of RAP materials reduces environmental harm and construction costs, besides it preserves the limited resources of stone, sand and gravel.