Granite Aggregate Research Articles

Three-dimensional mesoscopic investigation on the dynamic compressive behavior of coral sand concrete with reinforced granite coarse aggregate (GCA)

In the construction of island and reef engineering, coral concrete shows a good application prospect due to its abundant raw materials. However, the porous and fragile mechanical characteristics of coral reefs limit their use as coarse aggregate in the preparation of coral concrete materials. This study utilized hard and dense granite as the coarse aggregate and regarded coral sand concrete as a two-phase composite material consisting of spherical granite coarse aggregate (GCA) and coral mortar. It investigated the enhancement effect of granite on coral concrete from a microscopic perspective. Five 3D mesoscopic models with different GCA contents and randomly distributed aggregates were established to reveal the variation patterns and failure mechanisms of coral sand concrete under impact loading with GCA. The findings demonstrate that the K&C model can effectively simulate the dynamic compression behavior of coral mortar and granite materials. Under the action of a half-sine incident wave, the dynamic compressive strength of the samples increases with the increase in GCA, demonstrating that the addition of GCA can effectively enhance the impact resistance of coral sand concrete. As the content of GCA increases, the sensitivity of the samples to the loading wave amplitude also increases accordingly.

Comparison of fracture behavior of set concretes based on natural and crushed aggregates

Abstract The studies were carried out to diagnose the effects of coarse aggregate type on the mechanical behavior of plain concretes under incremental loading. During the studies mechanical parameters including compressive strength (fcm) and splitting tensile strength (fctm), as well as fracture parameters involving critical stress intensity factor (K_Ic^S) and critical crack tip opening displacement (CTODc) were evaluated. Crushed aggregates covered: basalt (BA), granite (GT) and limestone (LM) and natural peeble gravel aggregate (GL) were used in the concrete mixtures. The composite made on pebble aggregate acted as a reference concrete, as it were, in the analysis of the test results. For better understanding of the crack initiation and propagation in concretes with different coarse aggregates, a macroscopic failure surfaces examination of the tested beams is also presented. Both of the analyzed fracture mechanics parameters, i.e. 〖 K〗_Ic^S and CTODc increased significantly in the case of concretes which were manufactured based on crushed aggregates. They amounted in comparison to concrete based on gravel aggregate at levels ranging from 20% for concrete with limestone aggregate, to over 30% for concrete with a granite aggregate, and to as much as over 70% for concrete with basalt aggregate. Moreover, a clear correlation in the changes in the obtained results between the main strength parameters and fracture mechanics parameters was observed. The fracture process in each series of concrete was: quasi-plastic in the case of gravel concrete, semi-brittle in the case of limestone concrete, and clearly brittle in the case of the concretes based on granite and basalt aggregate. The results obtained help to explain how the coarse aggregate type affects the strength parameters and fracture toughness at bending.

Effect of Coarse Aggregate Type on the Fracture Toughness of Ordinary Concrete

This research work aims to compare the strength and fracture mechanics properties of plain concretes, obtained from different coarse aggregates. During the study, mechanical parameters including compressive strength (fcm) and splitting tensile strength (fctm), as well as fracture parameters involving critical stress intensity factor (KIcS) and critical crack tip opening displacement (CTODc) were evaluated. The effect of the aggregates used on the brittleness of the concretes was also analyzed. For better understanding of the crack initiation and propagation in concretes with different coarse aggregates, a macroscopic failure surfaces examination of the tested beams is also presented. Crushed aggregates covered were basalt (BA), granite (GT), and limestone (LM), and natural peeble gravel aggregate (GL) were used in the concrete mixtures. Fracture toughness tests were performed on an MTS 810 testing machine. Due to the high strength of the rock material, the rough surface of the aggregate grains, and good bonding in the ITZ area between the aggregate and the paste, the concretes with crushed aggregates exhibited high fracture toughness. Both of the analyzed fracture mechanics parameters, i.e., KIcS and CTODc, increased significantly in the case of concretes which were manufactured with crushed aggregates. They amounted, in comparison to concrete based on gravel aggregate, to levels ranging from 20% for concrete with limestone aggregate to over 30% for concrete with a granite aggregate, and to as much as over 70% for concrete with basalt aggregate. On the other hand, the concrete with gravel aggregate showed the lowest fracture toughness because of the smooth surface of the aggregate grains and poor bonding between the aggregate and the cement paste. However, the fracture process in each series of concrete was quasi-plastic in the case of gravel concrete, semi-brittle in the case of limestone concrete, and clearly brittle in the case of the concretes based on granite and basalt aggregates. The results obtained help to explain how the coarse aggregate type affects the strength parameters and fracture toughness at bending.

The role of nanomaterials in enhancing adhesion properties between bitumen and aggregate particles

During production and construction stages of asphalt mixtures, rheology of bitumen must be set at certain level. In addition, the adhesion strength between bitumen and the aggregate particles should be high enough so that during the service life of the pavement, asphalt mixture can resist various distresses. There are different methods of controlling rheological properties of bitumen binders and increasing adhesion properties of asphalt mixtures. One of the most effective methods of modifying bitumen binders of asphalt mixtures is using nanomaterials. In this research, two bitumen types of 60/70 and 85/100 penetration grades, three aggregate types (limestone, siliceous, and granite) and four nanomaterials types (nanohydrated lime NHL, nanosilica NSiO2, nanolime NCaCO3, and nanoclay bentonite NClay) were used at 2, 4, and 6% of the weight of bitumen. X-ray diffraction and X-ray fluorescence tests were performed and, microscopic images of thin-sections of aggregates and asphalt mixtures were taken with the aim of evaluating petrographic properties of aggregates and bonding characteristics of the bitumen binders with aggregate particles. Physical and rheological properties of the nano-modified bitumen binders were evaluated, performing dynamic shear rheometer and rotational viscometer tests. Boiling water and pull-off tests were also carried out in order to investigate the coating ability and the adhesion strength that is performed at the aggregate surface in the interface with the bitumen binders. Digital images were analyzed using Digimizer Software. The results indicated that the addition of nanomaterials at certain optimal percentage affected viscosity and improved rheological behavior of the bitumen binders at different temperatures, and increased adhesion properties of the bitumen coating the aggregate particles. Comparing the effects of different aggregates, it resulted that the binder coating the limestone aggregates performed better than the siliceous and the granite aggregates. The adhesion and the rheological properties of the 60/70 pen bitumen that was modified with nanomaterials were better than those of the 85/100 pen bitumen. Nano-modified binders at 4% NHL, or 2% NSiO2, or 4% NCaCO3, or 4% NClay exhibited the best behavior. Among these, the nano-modified binders containing 4% NHL resulted in better performance. Finally, the correlation between the adhesion and rheological behavior was suitable for nano-modified binders in order to improve the asphalt mixes' performance in operation and construction stages.

Replacement of conventional aggregates and fillers with steel slag and palm kernel shell ash in dense-graded asphalt mixtures

Large quantities of steel slag and palm kernel shell ash (PKSA) – waste products from steel production and palm oil milling, respectively – are generated annually in several countries, and their disposal is challenging. Meanwhile, the over-reliance on conventional rock aggregates for asphalt mixture production poses increasing sustainability challenges. This study investigated the potential of entirely replacing granite aggregates with steel slag and PKSA in a dense-graded asphalt mixture. Two sets of asphalt mixtures were prepared; the control mixture contained crushed granite aggregate and hydrated lime, while the other set incorporated steel slag as coarse aggregate and PKSA as fine aggregate and filler. Both mixture types utilized AC-30 viscosity-graded asphalt binder. The properties of the waste materials met the quality standards required for aggregates in asphalt mixture production. Both mixture types were designed according to the Marshall design procedure and were evaluated for durability (Cantabro abrasion loss), fatigue cracking Resistance, rutting Resistance, and moisture damage susceptibility. The Cantabro abrasion loss test indicated that the waste-based mixture was 3% less durable than the control. However, the cracking Resistance of the waste-based mixture was approximately twice that of the control. Even though the rapid rutting test indicated that the control mixture was slightly superior in rutting Resistance, the Marshall quotient suggested otherwise. Both mixture types exhibited similar moisture damage resistance. Overall, the steel slag and PKSA samples have shown high potential to replace virgin granite aggregates and lime in asphalt mixtures fully and are, thus, recommended for field performance evaluation and possible adoption.

Fracture characteristics of SMA mixtures with hydrated lime through the semi-circular bending approach

Stone Mastic Asphalt (SMA) is a composite mixture made up of high-quality crushed stone, fine aggregates, an asphalt binder, and a significant percentage of mineral filler in contrast to conventional mixtures. Renowned for its durability and rolling resistance, it is predominantly employed as a surface “wearing” course on main roads subjected to heavy traffic, but it can also be used as a binder course under specific project requirements. In this study, we investigated the effect of hydrated lime as a partial replacement of limestone filler at various concentrations on the mechanical and cracking resistance characteristics of 10-mm SMA mixtures. The semi-circular bending (SCB) test, which is pivotal for understanding the cracking mechanism was used to assess the mixtures performance-related response to this distress type. The mixture cores were produced with granite aggregates, limestone filler as natural filler, hydrated lime as natural filler replacement, and a 30/45 penetration asphalt type. Mixtures containing 1.1 %, 2.2 %, and 3.4 % of hydrated lime by weight of aggregates were evaluated, in addition to a control mixture without hydrated lime. The factors considered for comparing the mixtures included: load and deformation curves, stiffness, fracture toughness, fracture energy, and flexibility index of the mixtures. The experimental program also comprised a set of various test temperatures (0°C, 10°C, and 20°C) to better understand the cracking mechanism. Experimental results indicated a significant performance-dependency on the HL concentration and the test temperature. Precisely, it was found that the mixture with the highest hydrated lime content (3.4 %) exhibited the best cracking performance at 0°C and 20°C, making it a suitable filler replacement concentration. However, at 10°C, the mixture containing 2.2 % hydrated lime showed the most consistent performance overall, suggesting and important improvement in asphalt mixtures’ cracking resistance. Overall, these findings obtained from the SCB test approach substantiate the potential benefit of hydrated lime filler replacement in optimizing the cracking performance and durability of SMA mixtures under varying temperature conditions and loading regimes.

Proposal for formulation of blocks to guarantee the sustainability of buildings in the Abidjan real estate park

A recurring fall of buildings in recent years (2013-2023) in the city of Abidjan has caused enormous material and human damage. This study was initiated in order to propose a formulation for the development of concrete blocks to guarantee the sustainability of buildings in the Abidjan real estate. The raw materials used are aggregates composed of sand, granite powder and a hydraulic binder (portland cement) then water for mixing. The aggregates were characterized before being used for the manufacture of the various FSB, FPS and FPG concrete blocks. The materials were subjected to physical and mechanical tests. The results showed that the sand and granite powder aggregates have a granular class of 0/1 and 0/2 respectively. Concerning concrete blocks, the density increases with the maturation time, namely 28 days maximum and when they are composed of both sand and granite powder (FPS). This significantly reduces the number of pores in the material. The compressive strength test showed that at 28 days of maturation, the FPS are more resistant than the FPG and FSB with respective values of 6.50 MPa; 5.31 MPa and 3.10 MPa. It appears that the addition of granite powder to the composition of the concrete blocks improves the density, porosity and compressive strength of the latter. The promotion of this formulation among concrete block manufacturers would make it possible to improve real estate construction, guarantee the durability of buildings in the Abidjan real estate park and thus avoid the possible fall of buildings.

Analysis of the Impact of Superplasticizer on the Compressive Strength of Periwinkle Shell Concrete

This research project investigates the compressive strength characteristics of superplasticized concrete incorporating periwinkle shell (PS) as partial replacements for granite coarse aggregate. The study aims to assess the influence of superplasticizer content and curing age on the compressive strength development of the novel concrete mixtures. Comparative analysis with plain concrete (control specimen) reveals that superplasticized concrete with periwinkle shell partial replacement exhibits a slower strength development. Results indicate that the compressive strength of superplasticized PS concrete attains its maximum strength (22.07 kN/mm²) at 21 days with a 15% partial replacement and 0.5% superplasticizer content. The findings suggest that optimal strength development for PS partial replacement performs best at higher percentages (15%). Concerning the workability of fresh concrete, PS partial replacement exhibits a consistent increase in slump values with higher percentages of replacement and superplasticizer content, peaking at 55mm at 15% partial replacement and 1.5% superplasticizer content. This study contributes valuable insights into the optimization of compressive strength and workability of superplasticized concrete with PS partial replacements, offering a sustainable and resource-efficient alternative to conventional concrete mixtures

Properties of concrete with brick waste aggregate

The properties of concrete with brick waste aggregate are considered and it is established that as the amount of large aggregates - brick waste - increases, an increase in the water-cement ratio is observed. The mobility of concrete with a brick waste content of 50% corresponds to class P1, at 40% – P2, at 35% – class P3. Increased water consumption is necessary due to the effect of water absorption of porous brick chips, as well as maintaining the mobility of the concrete mixture, which changes significantly quickly over time. The initial settlement of the concrete mixture cone is 14–15 cm, after 40 minutes it decreases to 3–6 cm, and after 1 hour the mixture completely hardens. An increase in the content of coarse fillers leads to a decrease in the compressive strength of ceramic concrete. Thus, concrete samples with a filler content of 35% can be classified as class B27.5, samples with 40% – to B25, and 50% – to class B22.5. Electron microscopy was used to study the contact zone “cement stone – aggregate” on samples with crushed stone from brick waste and crushed granite aggregate. The results revealed that the adhesion strength of the aggregate to the cement stone is significantly higher than the strength of the aggregate itself, and the high surface roughness of lightweight secondary aggregates from broken bricks ensures good adhesion between the cement stone and the aggregate. In addition, the increased deformability of the aggregate reduces the negative impact on the shrinkage of cement stone, which has a positive effect on the structure of concrete, preventing the appearance of shrinkage microcracks.

Moisture Sensitivity Performance of Hot Mix Asphalt Mixture Incorporating Fly Ash Geopolymer (FAG) Asphalt Binder

In Malaysia, Hot Mix Asphalt (HMA) is widely used in asphalt production. HMA is a mixture of asphalt and aggregates that give durability to the road surface for pavement. Due to vehicles excessive traffic loadings that cause road surface damage, this pavement technology frequently undergoes maintenance and rehabilitation work. This study used recycled material as a modified binder and showned the best result in increasing stiffness and better rutting performance with high percentages of additives. This research focuses on the effect of FAG additive on asphalt mixture performance evaluation according to SuperpaveTM mixes design method. The procedures were specified according to the American Association of State Highway and Transportation Officials (AASHTO), American Society for Testing and Materials (ASTM), British Standard (BS) and Malaysian Standard (MS). The granite aggregate type was produced by a local quarry with conventional asphalt binder grade 80/100 and 60/70. Incorporation FAG in modified asphalt binder as levels of 0, 3, 5, 7, 9, and 11% by mass of asphalt binder. The performance of moisture sensitivity showed low moisture damage susceptibility for the mixture based on consistent values of TSR, in which all the specimens met the minimum TSR threshold of 80%. The optimization findings indicated that 9% of fly ash geopolymer might be the ideal content for modifying the asphalt binder. Overall, research findings suggest that using geopolymers may have improved some of the characteristics of asphalt binder and the performance of asphalt binders in pavement applications. Thus, the outcomes of this research were significantly used for further performance test and analysis on the asphalt mixture.

The Influence of Basalt Aggregate on The Mechanical Performance of Hot Mix Asphalt (HMA) Mixtures

The increasing of traffic load within years reduced the ability to withstand the load path structure, stiffness and strength of the pavement. Along with the development in heavy traffic volume on roads, particularly in tropical locations, the rutting impact has emerged as one of the most significant failures in recent years. A great deal of research has been done to improve the durability and long-term performance of asphalt mixtures in dynamic environments. This paper investigates the effect of basalt aggregate on the improvement of rutting and moisture performance of hot mix asphalt (HMA) mixtures. In this respect, Marshall mix design was employed in the preparation of the specimens. Dynamic creep and moisture susceptibility test have been carried out to evaluate the mechanical properties of the HMA mixture with 30%, 50% and 100% of basalt aggregate replacement. As a result, the performance (creep modulus, permanent deformation and tensile strength) of modified HMA improved remarkably 40- 90% with replacement of 50% basalt aggregate. Based on this studies, the basalt aggregate and its combinations with granite aggregate in asphalt mixes has a significant effect on mechanical properties of HMA mixtures.

Performance Research of Cement Concrete Pavements with a Lower Carbon Footprint.

The growing interest in the use of building materials with a reduced carbon footprint was the aim of this research assessing the impact of four different types of low-emission cements on the properties of cement concretes used for the construction of local roads. This research work attempted to verify the strength characteristics and assess the durability of such solutions, which used the commonly used CEM I 42.5 R pure clinker cement and three multi-component cements: CEM II/A-V 42.5 R, CEM III/A 42.5 N-LH/HSR/NA, and CEM V/A S-V 42.5 N-LH/HSR/NA. Cement was used in a constant amount of 360 kg/m3, sand of 0/2 mm, and granite aggregate fractions of 2/8 and 8/16 mm. This research was carried out in two areas: the first concerned strength tests and the second focused on the area of assessing the durability of concrete in terms of frost resistance F150, resistance to de-icing agents, water penetration under pressure, and an analysis of the air entrainment structure in concrete according to the PN EN 480-11 standard. Analyzing the obtained test results, it can be concluded that the highest compressive strength of more than 70 MPa was obtained for CEM III concrete, 68 MPa for CEM V concrete, and the lowest for CEM I cement after 90 days. After the durability tests, it was found that the smallest decrease in compressive strength after 150 freezing and thawing cycles was obtained for CEM III (-0.9%) and CEM V (-1.4%) concretes. The high durability of concrete is confirmed by water penetration tests under pressure, because for newly designed recipes using CEM II, CEM III, and CEM V, water penetration from 17 mm to 18 mm was achieved, which proves the very high tightness of the concrete. The assessment of the durability of low-emission cements was confirmed by tests of resistance to de-icing agents and the aeration structure performed under a microscope in accordance with the requirements of the PN-EN 480-11 standard. The obtained analysis results indicate the correct structure and minimal spacing of air bubbles in the concrete, which confirms and guarantees the durability of concrete intended for road construction. Concretes designed using CEM V cement are characterized by a carbon footprint reduction of 36%, and for the mixture based on CEM III, we even observed a decrease of 39% compared to traditional concrete. Concrete using CEM II, CEM III, and CEM V cements can be successfully used for the construction of local roads. Therefore, it is necessary to consider changing the requirements of the technical specifications recommended for roads in Poland.

Mechanical properties and damping characteristics of Egyptian granite-epoxy composite material

Vibrations generated during the operations of machine tools, especially at high-speed operation impact several issues in machined parts such as imprecision dimensions and a poor surface finish. This prompts research and studies into alternative materials for machine tool structures to provide considerable damping performance and acceptable stiffness compared to traditional materials. This paper deals with the experimental study of a developed granite-epoxy composite, made from waste granite and local epoxy as an alternative material for machine tool structures. A waste of Egyptian Red Aswan granite was used as filler after being crushed and sifted into three sizes: fine (less than 1 mm), medium (1 to 5 mm), and coarse (5 to 8 mm). A local commercial epoxy resin kemapoxy 150 was added to a granite aggregate mixture having grain proportions 50:25:25 for fine, medium, and large, respectively. The influence of the variation of the epoxy weight ratio on the static and damping characteristics of a proposed granite–epoxy composite material was experimentally investigated. To ensure a coherent granite-epoxy composite, the required minimum resin content of 13.88 wt% was determined, and the granite/epoxy ratios were selected as 85:15 wt%, 80:20 wt%, and 75:25 wt%. The findings exhibit that the largest compressive strength of 76.8 MPa and the greatest flexural strength of 35.4 MPa is achieved at the highest epoxy weight ratio of 25%. The largest damping ratio of 0.0202 is observed at the epoxy ratio of 20% and it decreases to 0.015 when the epoxy ratio is increased to 25%. An Egyptian granite-epoxy composite, made from waste granite and local epoxy, is a promising alternative material for machine tool structures. It offers both economic and environmental benefits, along with high mechanical and damping properties compared to traditional machine tool materials.

Analysis of Microwave-Induced Damage in Granite Aggregates Influenced by Mineral Texture

The use of microwave energy to recycle high-quality coarse aggregates from waste concrete or assist hard rock breakage in underground building engineering is promising. Controlling or promoting the damage of coarse aggregates, i.e., hard rocks, under microwave irradiation is a crucial issue faced by these techniques. Understanding the damage mechanisms of hard rocks exposed to microwaves is thus urgent. Fracture toughness is a significant mechanical parameter of rocks that reflects their ability to resist crack propagation and damage evolution. In this study, the fracture toughness degradation of microwave-heated granite was investigated by combining experimental investigations and numerical simulations. A three-point-bending (TPB) experiment was conducted on granite specimens after microwave irradiation. A coupled electromagnetic–thermal–mechanical model considering the actual mineral texture of the granite specimen was established. The evolution of the temperature gradient and stress field near the initial notch tip were investigated. The results suggest that the microwave-induced maximum temperature gradient and stress in granite are at the plagioclase–quartz (Pl–Qtz) interfaces or inside the Pl near the boundary. The region of cracking initiation was defined as the damage zone, which could be obtained by comparing the microwave-induced thermal stress with the critical value. The fracture toughness degradation, which corresponds to the evolution of the damage zones, can be divided into two stages. A relatively rapid decrease in fracture toughness in the first stage is primarily caused by the spread of the scattered damage zones along the Pl–Qtz interfaces; subsequently, a gentler fracture toughness degradation results mainly from the extension of the previous damage zones.

Comparative analysis of lateritic and granitic aggregates in asphalt mixtures: morphological properties and performance implications

Comparative analysis of lateritic and granitic aggregates in asphalt mixtures: morphological properties and performance implications

Influence of substituting aggregates on the characteristics of high-strength concrete

High-strength concrete (HSC) is a specialized form of concrete that possesses enhanced compressive strength compared to conventional concretes. In the initial phase of the experimental study, silica fume and metakaolin were utilized as additional supplementary cementitious materials in various percentages ranging from 6% to 12% for making different trails to obtain the concrete mix with high strength. Test results indicated that trail mix having 10% silica fume and metakaolin gave the desired strength. The second phase of the study incorporates the utilization of crushed granite coarse aggregates at varying replacement ratio ranging from 0 to 100%, serving as a substitute for natural aggregates. Test results demonstrated the better quality of crushed granite aggregates in contrast with locally available natural aggregates, enhanced strength properties of concrete including compressive strength, split tensile strength, Flexural strength, etc at each replacement percentage, thus suggesting the use of crushed granite a favorable option for obtaining high strength concrete.

Statistical Reliability Analysis of Ultrasonic Velocity Method for Predicting Residual Strength of High-Strength Concrete under High-Temperature Conditions.

Herein, we conducted a comprehensive statistical assessment of the ultrasonic pulse velocity (UPV) method's effectiveness in predicting concrete strength under diverse conditions, specifically early age, middle age, and high-temperature exposure. The concrete mixtures, with water-to-cement (W/C) ratios of 0.33 and 0.28, were classified as granite aggregate or coal-ash aggregate mixes. Compressive strength and UPV measurements were performed under these conditions, and subsequent statistical analyses treated the identified factors as distinct groups. The results revealed a substantial difference in compressive strength between specimens at early age (average of 13.01) and those at middle age (average of 41.96) and after high-temperature exposure (average of 48.08). Conversely, UPV analysis showed an insignificant difference between the early-age specimens and those after high-temperature exposure. The analysis of the W/C ratio and coarse aggregate demonstrated significant differences (p-value < 0.05) in compressive strength between specimens in middle age and those exposed to high temperatures, excluding the early-age specimens. However, UPV analysis revealed insignificant differences, with p-values of 0.67 and 0.38 between specimens at an early age and post-high-temperature exposure, respectively. Regression analysis identified suitable functions for each scenario, emphasizing the importance of a strength prediction model for concrete after high-temperature exposure, particularly considering the W/C ratio. Since concrete showed statistically different compressive strength, UPV, and strength prediction models in three conditions (early age, middle age, and high temperature), different strength prediction models must be used for the purpose of accurately predicting the strength of concrete.

Evaluation of residual bond behaviour between rebar and recycled aggregate concrete after high-temperature exposure followed by water spray cooling

This paper presents an evaluation of the residual bond behaviour between rebar and recycled aggregate concrete (RAC) using granite natural coarse aggregates and different recycled coarse aggregate (RCA) replacement levels (δ = 0%, 30%, 50%, and 100%) for both pull-out and cubic specimens. After high-temperature exposure (T = 200, 400, and 600 ℃) followed by water spray cooling, the results revealed a consistent decline in bond strength and compression strength with increasing temperature. Compared to ambient conditions, bond strength and compression strength decreased by 65.2% ∼ 77.8% and 53.2% ∼ 58.4%, respectively, after exposure to 600 ℃. The reduction rate of residual bond strength changed significantly at about 400 ℃. There was a linear relationship between RAC compression strength and rebar–RAC bond strength after high temperature exposure followed by water spray cooling. With increasing RCA replacement levels, the relative bond strength gradually improved at the same temperature. Based on the regression analysis, empirical formula for the rebar–RAC bond strength and bond–slip relationship models were proposed, all taking into account RCA replacement levels and temperature.

Comparative Study of the Crushing Strengths of Recycled Coarse Aggregates Concretes and Natural Aggregates Concretes

Recycled Coarse Aggregate (RCA) is a recycled concrete material from construction sites, which is being reused for fresh concrete production. The use of this material reduces quarrying of Natural Coarse Aggregate (NCA). Properties of RCA are variable depending on the properties of parent concrete. In a fast-growing economy, the generation of construction waste has increased considerably, and social and environmental concerns on recycling the waste have accordingly increased. Construction Engineers have resorted to recycling these demolition wastes to maintain a friendly green environment. This study compared the crushing strengths of Recycled Coarse Aggregate concrete with Natural Aggregate concretes. The RCA was obtained from demolished drains and culverts while the Natural Coarse Granite Aggregate was from Akamkpa, Cross River State, Nigeria. Using RCA and NCA of maximum size 20mm, concrete cubes were prepared for compressive strength tests. Other properties of the aggregates were determined. Three mix proportions of 1:1½:3, 1:2:4 and 1:3:6 at water cement ratio of 0.6 were utilized and the specimens were tested at curing ages of 7, 14, 21 and 28 days. Results indicated that RCA produced concretes with strengths lower than those using NCA. RCA concretes also had slumps lower than those of NCA concretes.

An analytical approach to deduce loading rate-sensitivity of fracture mode of concrete and mortar

The fracture of two-component solids is considered in order to study the sensitivity of the failure mode to the loading rate. The incubation time approach, supplemented by the randomized Sign-Perturbed Sums (SPS) method, is applied to develop an analytical model to predict the difference in the fracture pattern under dynamic and static conditions. To verify and validate the model, experimental data of dynamic tests on concrete, mortar and granite aggregate are analyzed. It was demonstrated that the model indicates the change in the failure mode for inhomogeneous material such as concrete, while the analysis results for pure granite do not predict the same phenomenon. The results obtained are in agreement with the experimentally observed change in the fracture mechanism of concrete from transgranular to intergranular as the loading rate decreases. Thus, it was shown that the developed model is able to predict the change of the fracture mechanism with the increase of the loading rate.