Reduction In Compressive Strength Research Articles

Experimental evaluation of shrinkage properties in concrete incorporating coal mine waste rock

This research investigates the properties of concrete utilizing coal mine waste rock (CMWR) as a substitute for river sand. The workability of fresh concrete is assessed through slump tests, revealing a decrease in a slump as the percentage of CMWR replacement increases. The density of the concrete mixtures increased with curing time, and the compressive strength also exhibited an upward trend but with lower values compared to the control concrete when CMWR was used as a replacement. The reduction in compressive strength ranges from 11.4% to 47.6% for CMWR replacement levels of 25% to 100%. The study also examines the influence of climate conditions, including temperature and humidity. Shrinkage deformation tests indicate that CMWR concrete demonstrates higher plastic and dry shrinkage than river sand concrete. CMWR concrete exhibits significantly higher drying shrinkage, attributed to the enhanced water absorption capacity of CMWR particles. These findings provide valuable insights into the performance of concrete incorporating CMWR and propose potential strategies for mitigating its effects. The research outcomes contribute to the knowledge base in the field and offer practical implications for the operation of CMWR in concrete applications

Upcycling end-of-life bricks in high-performance one-part alkali-activated materials

One-part alkali-activated materials (AAMs) can preserve natural resources and lower embodied carbon of the built environment by accommodating various wastes, industrial by-products, and end-of-life materials in their composition. This study investigates the feasibility of using end-of-life bricks in two physical states, powder and aggregate, to partially replace fly ash precursor and natural aggregate in AAMs, respectively. The mechanical characteristics, microstructure, water absorption, freeze-thaw and fire resistance of the modified AAMs were evaluated. The effect of adding different ratios of nano graphite platelets was also investigated. Results showed that brick-based one-part AAMs can achieve mechanical properties, pore structure, water absorption and freeze-thaw resistance comparable to fly ash-based AAM while having 65% better fire resistivity. Incorporating bricks as aggregate resulted in a maximum improvement of 17% and 27% in the AAMs' compressive and flexural strength levels, respectively, and a general enhancement in the freeze-thaw resistance with showing no reduction in compressive strength after exposure to elevated temperature. Incorporating 0.1 wt% nano-graphite further enhanced flexural strength by 30%, decreased water absorption by 18% and improved freeze-thaw resistance compared to the mix without nano-graphite. Moreover, adding up to 0.5% nano-graphite enhanced the fire resistivity of the composite, allowing it to exhibit 19% better strength performance than before exposure.

Hydrochloric acid resistance of mortars incorporating waste glass powder as cementitious materials

AbstractDespite numerous studies conducted on the potential of waste materials as cement substitutes, the resistance of mortars comprising such blended cementitious materials against acidic environments has seldom been investigated. This paper presents an investigation into the potential of waste glass powder (WGP) as a replacement for cement in enhancing the mechanical, and durability of cementitious materials subjected to acidic environments. The study examines the impact of WGP on the resistance of mortar to hydrochloric acid solution attack, with specimens containing 0%, 5%, 10%, 15%, 20%, 25%, and 30% WGP produced as cement substitutes. The tests were conducted on the cement mortar and paste after water curing for 7, 14, 28, 42, and 56 days. Initially, the pozzolanic activity index assessment, fresh density, water absorption, and compressive strengths during water curing times were evaluated. Subsequently, the performance of mortars, when subjected to hydrochloric acid solutions, was assessed, including mass loss, residual compressive strength, visual inspection, and microstructure features during 8 weeks of immersion in hydrochloric acid. The results of the study indicated that the incorporation of WGP led to improved hydrochloric acid resistance in the mortar. Furthermore, an increase in WGP content resulted in a reduced reduction in compressive strength against hydrochloric acid attacks as the ages progressed. The study revealed that the mortar containing 5% WGP as a cement substitute had the highest compressive strength compared to other specimens, and using 10% WGP as a supplementary cementitious material was comparable to the control mixture. Finally, the x‐ray diffraction pattern indicated that the specimen containing 5% WGP had a lower intensity of portlandite peaks than the reference specimen.

Mechanical properties, flexural behaviour, and ductility characteristics of fibre-reinforced geopolymer mortar

This study aims to explore the potential of ambient-cured geopolymer as a substitute for ordinary Portland cement (OPC)-based mortar. However, due to their brittle nature, geopolymer materials require reinforcement to enhance ductility. To address this, an experimental program was conducted to investigate the effects of adding polypropylene (PP) and micro steel (MS) fibers to fiber-reinforced geopolymer mortar (FRGM) at volume fractions of 0%, 0.5%, 1%, and 1.5%. The ternary blended geopolymer mortar consisting of fly ash (FA), and ground granular blast furnace slag (GGBS), along with a novel pozzolan called eco-processed pozzolan (EPP) was investigated. The present study assessed the hardened properties of the FRGM, including compressive strength, splitting tensile strength, modulus of elasticity (MoE), ultrasonic pulse velocity (UPV), and the compressive strength of the material when exposed to elevated temperatures. The aim of this study was also to investigate the load–deflection response in terms of deflection, load, flexural strength, and toughening mechanisms; and also, the bonding between the fibers and the mortar matrix was examined using field emission scanning electron microscopy (FESEM). The results indicated that including 0.5% PP fibers and up to 1.5% MS fibers marginally improved compressive strength and MoE. The corresponding increments in splitting tensile strengths were 5% and 134%, respectively. The addition of fibers improved the fracture parameters of the FRGM. The inclusion of both MS and PP fibers significantly enhanced post-cracking flexural and toughness energy. At deflection L/150, MS fiber mixes exhibited 4–5 times higher toughness energy than PP fiber mixes, and also its evidently observed in the FESEM micrographs. The incorporation of 1.5% fiber volume to non-fibrous mix resulted in an improvement of 43.2 N.m. and 10.1 N.m. in toughness (T150) for MS and PP mixes, respectively. At an elevated temperature of 600 °C, the FRGM specimens gained a massive reduction in compressive strength, with the maximum result being at 87% for 1.5PP and 71% for 0.5MS. Overall, the MS fiber-reinforced geopolymer mixes exhibited superior performance as compared to PP fibers.

Utilization of broken rock in shallow gobs for mitigating mining-induced water inrush disaster risks and environmental damage: Experimental study and permeability model

Coal mining-induced groundwater losses may trigger water inrush disasters and surface ecological degradation. The compaction and seepage characteristics of broken rock in gobs can be used to find the balance point of water inrush prevention and water resource protection in shallow coal seam groups. These characteristics, as well as geological and engineering parameters of shallow coal seam mining, are experimentally determined in this study. The performed permeability tests revealed that the percentage of voids in broken rock exponentially decreased with the axial stress. The water seepage of broken rock in the compaction process conformed to the Forchheimer theory, with the permeability ranging from 10−1 to 10 D. The initial value and reduction range of mudstone permeability in the three lithologic samples were the smallest. The uniaxial compression strength reduction caused by the increase in unit mass water due to water saturation of natural rock samples were 5.8 and 3.2 % for coal and sandstone, respectively. Based on the experimental results on compaction and seepage of broken rock, the axial stress-percentage of voids-permeability model considering compaction and re-crushing was established. The mudstone roof was found to be the key rock stratum during re-mining for ecological protection and hydraulic connection evaluation of the overburden.

Numerical modelling of microwave irradiated rock fracture

Rock fracturing through microwave irradiation has received significant attention recently as a viable pretreatment for improving the energy efficiency of comminution processes. This study presents a numerical analysis on the effects of microwave heating on the mechanical properties of hard rock. In particular, the reduction of the uniaxial compressive and tensile strength of granite-like rock due to microwave irradiation induced damage is numerically assessed.Rock fracture is modelled by a damage-viscoplasticity model, with separate damage variables for tension and compression types of failure. A global solution strategy is developed where first the electromagnetic problem is solved in COMSOL multiphysics software, then its solution is used as an input for the thermo-mechanical problem, which is finally solved by means of a staggered explicit solution method. Due to the preeminence of the thermal radiation, the thermal and the mechanical parts of the problem are considered as uncoupled.The model behaviour is tested in 3D finite element simulations of three-mineral numerical rock specimens, with mesostructures explicitly defined, pretreated first in a microwave oven and then subjected to uniaxial compression and tension tests. The results show that the compressive and tensile strength of rock can be considerably reduced by the microwave irradiation pretreatment.

Developing fired clay bricks by incorporating scrap incinerated waste and river dredged sediment

The global extraction of several billions of clean clay resources, which destroy millions square meters of land, is triggering environmental problems. Incorporating different dosages of incinerated waste or dredged sediment in bricks production has been studied by many researchers. Research articulating the combined effect of incinerated waste material (IWM) and river dredged sediments (RDS) addition on the performance of bricks is scarce. This paper aims to present findings on the engineering performance of fired bricks developed with the addition of IWM and RDS. In this regard, bricks were made with 5 wt% IWM and different dosages of RDS (i.e., 0 – 15 wt%). Physical, durability, mechanical, thermal and microstructure of the developed bricks is examined. Bricks’ shrinkages were found meeting quality performance criterion in the 1.42 – 4.11% range. The highest bulk density of 1.85 g/cm3 permit to classify bricks obtained as lightweight. Water absorptions were mostly within the acceptable 20% tolerance level postulating the developed bricks high durability standard. Compressive strength reductions, which were confined within 5.28 and 21.57 MPa, showed the developed bricks applicability to structural weight-supporting construction as well as specialized engineering construction works. The 40.5% thermal conductivity reduction in WB15 bricks (at 800 °C) theorized its suitability for thermal insulation construction. Mineralogical and morphological analyses of fired bricks clearly showed kaolinite polymorphic phase transformation, which contributed to the different morphologies in the brick matrices. Consequently, reuse of IWM and RDS offered a chance to advance sustainable use of scarce clay resources in lightweight and thermal insulation brick production.

Properties of mortar containing Phragmites Australis Ash

Purpose The purpose of this paper is to examine the use of phragmites australis ash (PAA) in cementitious systems to achieve sustainable construction. Design/methodology/approach In this paper, the properties of mortar containing PAA as partial cement replacement are determined. The PAA is produced through slow burning in a closed system to minimize the CO2 emission. A total of four mortar mixes are prepared with PAA replacement levels ranging from 0% to 30% by weight. The water to binder and the proportions of binder to sand are 0.55 and 1:3 by weight, respectively. The properties tested are density, compressive strength, flexural strength, ultrasonic pulse velocity, water absorption by total immersion and capillary rise. Testing is conducted at 1, 7, 28 and 90 days. Findings While there is a decrease in strength as the amount of PAA increases, there is strong indication of pozzolanic reaction in the presence of PAA. This is in agreement with the results reported by Salvo et al. (2015), where they found noticeable pozzolanic activities in the presence of straw ash, which is rich in SiO2 and relatively high K2O content. At 90 days of curing, there is a decrease of 5% in compressive strength at 10% PAA replacement. However, at 20% and 30% replacement, the reduction in compressive strength is 23% and 32%, respectively. The trend in flexural strength and ultrasonic pulse velocity is similar to that in compressive strength. The water absorption by total immersion and capillary rise tends to increase with increasing amounts of PAA in the mix. There seems to be a linear relationship between water absorption and compressive strength at each curing age. Research limitations/implications The Phragmites australis plant used in this investigation is obtained from one location and this present a limitation as the type of soil may change the properties. Also one method of slow burning is used. Different burning methods may alter the composition of the PAA. Practical implications This outcome of this research will contribute towards sustainable development as it will make use of the waste generated, reduce the amount of energy-intensive cement used in construction and help generate local employment in the area where the Phragmites australis plant grows. Originality/value To the best knowledge of the authors, the ash from the Phragmites australis plant has not been used in cementitious system and this research can be considered original as it examines the properties of mortar containing PAA. Also, the process of burning in a closed system using this material.

Combined effect of fly ash and fiber on spreadability, strength and water permeability of foam concrete

Strength and permeability are the two critical properties of interest for various applications of foam concrete (FC). These properties are well known to be highly dependent on parameters such as density, mix composition and microstructure of FC. Among various measures to enhance the strength and permeation characteristics of FC, incorporation of fly ash and polypropylene fiber has been proven to be effective solutions by various studies. In terms of permeability, though the measurement of air/water permeability has been suggested by various methods, usually such measurements are limited to a pressure of 3 bar. For higher pressures (as recommended in codal provisions) no to limited work is available. In this paper, variation in spreadability, permeability, compressive strength and split tensile strength of FC due to replacement of 50% of sand with Class F fly ash and incorporation of polypropylene fiber is investigated on a systematic basis. For the measurement of permeability at higher pressures (>3 bar), use of novel sealing mechanism using 5 mm thick rubber membrane as sealant with iron spiral cylinder and clamp as casing, is attempted in this work. The present study is first of kind of study using the above-mentioned sealing mechanism for measurement of permeability of FC at higher pressures. Further, only scanty literature is available on permeation behavior of FC with fly ash (as filler) and polypropylene fiber. As per the present findings, particularly in lower density mixes (say density 1000 kg/m3) tested at age of 56 days, replacement of 50% of fine aggregate (by weight) by Class F fly ash results in 114% enhancement in compressive strength and 69% reduction in permeability. In addition, mixes with 0.05% of total solids replaced with polypropylene fiber (by weight) show 25% reduction in compressive strength and 500% increase in permeability in comparison to FC mixes without fly ash and polypropylene fibers. Thirdly, considering mixes with addition of fly ash and polypropylene fibers both, it is found that the effect of fly ash is more predominant from strength perspective than fiber. From permeability perspective however, the fibers control the permeability significantly due to their higher impact on microstructure of FC.

Dispersion of hydrophobic waste amorphous carbon powder in cementitious environment and its effect on the permeability of cement paste

A Proper dispersion of powder-based hydrophobic admixtures in cementitious composites is challenging due to the presence of water. Studies have shown that amorphous carbon powder (ACP), a hydrophobic by-product of refining waste materials of paraffin production can be used as a hydrophobic agent. However, mixing methods and dispersing agents for modifying cementitious materials with ACP can significantly impact their mechanical properties, workability, water-repellency (hence the durability), and dispersion quality of ACP. Lack of information about the extent of their impact on different aspects mentioned above can hinder the practical use of ACP as a hydrophobic agent. To fill this gap, the objective of this study is to comprehensively investigate factors in the dispersion of ACP in cementitious materials and the tradeoff between mechanical properties and water permeability of ACP-modified cementitious materials when more than one mixing method is adopted. The impacts of different dispersing agents and mixing methods, including ultrasonication, dry mixing, and after mixing, on dispersion quality of ACP in cementitious environment analogous with aqueous solutions and hardened cement paste were assessed. Polycarboxylate ether-based superplasticizer (PCE) proved to be the most effective dispersing agent. Compressive strength of ACP modified cement paste can be increased or decreased with or without the workability reduction effect of ACP along with PCE respectively. Based on volume fraction of ACP clusters in X-ray micro-CT 3D reconstruction of hardened cement paste, ultrasonication was identified as the most effective mixing method and dry mixing was the worst in terms of achieving a uniform distribution of ACP in cement paste. However, all mixing methods presented more than 85% volume fraction of uniformly dispersed ACP areas with no major difference in terms of hydrophobic modification capability. Modifying cement paste with a higher amounts of ACP (5 to 15% by weight of cement) substantially increased water contact angle (up to 171% for w/c ratio of 0.35) and decreased water absorption. The hydrophobic modification capability of ACP increases with a decrease in the quality of cement paste and is diminished by the presence of PCE. Consequently, without PCE, water absorption rate was reduced by up to 92% in similar ACP modified cement paste samples, which also led to a major reduction in compressive strength.

Concrete Blocks Using HDPE Solid Waste as Aggregate

The objective of this study was to analyze the addition of plastic as a partial component of the coarse aggregate in concrete, for the design of ecological blocks, establishing a linear equation that estimates the compressive strength of the block, varying the volumes of cement, sand, gravel and plastic. For the design of blocks, volume in three proportions were considered (cement/fine aggregate/coarse aggregate), thus four types of mix proportions were made (1/1/1, 1/1.25/2.5, 1/1.5/3 and 1/2/4). Coarse stone aggregate as a partial aggregate component was replaced by flake HDPE type plastic HDPE in proportions of 0, 25 and 50% coarse stone replacement. The compressive strength and unit weight of the concrete was measured after 30 days of curing. The research methodology was of a quantitative type of descriptive experimental design. The results showed that the addition of 25 and 50% plastic as a coarse aggregate reduced the unit weight of the concrete to 9.7 and 12.02% respectively. However, in this case, the reduction in compressive strength was up to 29.17 and 48.5% respectively for its best effectiveness, reducing only the unit weight of the parts.

Effect of fresh concrete compression technique on pre- and post-heating compressive behavior of steel fiber-reinforced concrete: Experiments and RSM-based optimization

Despite the many advantages of fresh concrete compression technique for improving the performance of hardened concrete under compression, no study has so far addressed various behavioral aspects of this type of concrete in different conditions and scenarios such as fire, which may occur during the service life for a structure made up of this concrete type. Here, the compressive performance of compressed concrete with steel fibers was addressed before and after experiencing elevated temperatures considering key variables including the volume quantity of steel fibers, diameter-to-thickness ratio of steel tube (mold), capacity of the reference concrete, and exposure temperature. To reach this goal, 60 concrete cylinders were tested under axial compression, and the results including the compressive strength, elastic modulus, strain at peak stress, toughness, axial stress–strain graph, and weight loss were assessed together with the results of a visual inspection, failure mode, and microstructure of concrete. The results demonstrated that although the fresh concrete compression technique notably improved the mechanical features of concrete, especially the compressive strength by up to 100 % at the ambient temperature, adding steel fibers, lowering the water-to-cement ratio (w/c), and using a tube with a thinner wall as the mold lowered the efficiency of this technique in improving the compressive performance. In addition, the amount of increase in concrete strength due to compressing the fresh concrete had a linear relationship with the amount of excess water removed from it. The positive impact of the fresh concrete compression technique on the concrete strength at high temperatures was significant. In this regard, the compressive strength reduction of the compressed concrete was 20 % lower than that of the uncompressed concrete. However, the fresh concrete compression technique was not very effective against the deterioration of the modulus of elasticity caused by high temperatures. Ultimately, the response surface method (RSM) was used to reach an optimum solution for the design variables that could maximize the compressive capacity of fibrous compressed concrete per different target temperatures.

A new heat resistant load bearing system incorporating honeycomb structured cementitious composite investigated via experiments and modelling

The load-bearing cementitious materials such as concrete rely on passive insulation to resist heat in fire and other high-temperature events. This study introduces a novel load-bearing system, incorporating a honeycomb-structured cementitious composite (HSCC) to enable adjustable active heat dissipation. Compared with passive thermal insulation, active heat dissipation brings substantial improvement on heat resistance performance under compressive load. The study investigated the heat transfer process of the HSCC material fabricated by 3D-printed micro scaffolds by combining the microscopic thermal imaging method and finite element simulation. The proposed material has a conductivity of up to 0.24 W/mK, which shows a 30% improvement in heat resistance compared to lightweight concretes. The total compressive strength reduction is ten times less than ordinary concrete under elevated temperatures at 1300 °C. The microscopic thermal imaging provided experimental data to enable the development of multi-phase simulation models, which allowed further predictions of the material performance under elevated temperatures. The novel load-bearing system enabled ventilation through the HSCC in combination with the low thermal conductivity of the HSCC, which allowed this novel system to demonstrate a capacity loss at 1300 °C that was ten times less than that of ordinary concrete walls. Furthermore, the effect of ventilation and heterogeneity in the HSCC on the heat dissipation and temperature distribution in the materials is also characterized by this study.

Investigation of alkali-silica reaction on mortars with alternative binder systems: Alkali activated Slags and Celitement

This study investigates the resistance against alkali-silica reaction (ASR) of two alternative binder systems, alkali-activated slag (AAS) and Celitement (Celite). Experimental studies on expansion and mechanical strength are carried out. Coupled kinetic and equilibrium thermodynamic modeling is used to clarify the role of binder chemistry on ASR. It was observed that under accelerated conditions OPC based mortars were more susceptible to ASR compared to AAS and Celite-based mortars. Based on experimental and modeling results, a correlation is shown between the dissolution of silica and the degree of expansion, but no correlation was found between the predicted amount of ASR products and the measured degree of expansion. Finally, the expansion degree could only be correlated with the reduction in compressive and flexural tensile strength for ASR-exposed samples.

Influence of calcium carbonate on green self-compacting concrete incorporating porcelain tile waste as coarse aggregate replacement

The disposal of ceramic tile waste poses a significant environmental challenge in the construction industry. This study aims to explore the influence of calcium carbonate (CC) on the properties of self-compacting concrete (SCC) incorporating porcelain tile waste as a coarse aggregate replacement. The objective is to enhance the performance of SCC while addressing the limitations of recycled ceramic aggregates and achieving the desired strength class. SCC specimens were cast by partially and completely substituting natural crushed rock with varying percentages of porcelain tile aggregates (PTA-0, 25 %, 50 %, 75 %, and 100 %) and cement with calcium carbonate (CC-10 %, 20 %, and 30 %). Workability assessments, mechanical properties, and durability were evaluated and compared against those of reference concrete. The experimental findings revealed that the incorporation of CC and PTA positively influenced the workability, mechanical properties and durability of SCC. Notably, the SCC mixture incorporating 10 %CC and 25 %PTA demonstrated exceptional performance, achieving the highest compressive strength of 64.9 MPa at 28 days. Moreover, even with complete substitution, the compressive strength reduction remained below 5 %. These results highlight the potential of PTA and CC-based SCC mixtures as an efficient and sustainable approach for utilizing porcelain tile waste in high performance concrete production. The findings contribute to addressing environmental concerns, promoting waste management practices, and reducing the reliance on natural resources in the construction industry.

Effect of siliceous sand volume fraction on the properties of alkali-activated slag mortars

One of the critical factors affecting the performance of alkali-activated slag (AAS) is the nature and dose of alkali activator. The activator type can play a significant role during the transition from pastes to mortars or concretes. Therefore, three basic sodium activators (water glass, carbonate, and hydroxide) of the same molarity of 4M Na+ were used to prepare AAS-based mortars with different volume fractions of siliceous sand. These were compared by means of workability, mechanical strength, and long-term shrinkage under autogenous conditions. The results were compared to those obtained on pastes with similar workability. Increasing the content of the sand tended rather to decrease the mechanical properties, while greatly decreased autogenous shrinkage. Nevertheless, the most remarkable differences for different activators were observed when comparing the mortars with pastes. The transition from pastes to mortars resulted in the highest reduction in both compressive and flexural strength for sodium hydroxide. The flexural strength of the mortars with sodium water glass and sodium carbonate even increased considerably in presence of sand.

Evaluation of copper slag and stainless steel slag as replacements for blast furnace slag in binary and ternary alkali-activated cements

Commonly used alkali activation precursors such as blast furnace slag and fly ash will soon become less available due to resource competition, and may cease to be produced in certain regions. This limitation in future supply is a main driving force for the investigation of alternative precursor sources, such as non-blast furnace slags and non-ferrous slags, to produce alkali-activated binders. The current study investigates the incorporation of copper slag (CS) and stainless steel slag resulting from electric arc furnace operations (EAFSS) as partial replacements for ground granulated blast furnace slag (GGBFS) in producing alkali-activated materials (AAMs), at paste level. Five binary alkali-activated mixtures with different replacement levels of GGBFS with CS, and three ternary mixtures with both CS and EAFSS as partial and total replacements for GGBFS, are activated by a sodium silicate solution. Replacing GGBFS with CS and EAFSS retards the reaction kinetics, resulting in improved fresh-state properties of the investigated AAMs, better retention of workability and longer setting times. The reaction of alkali-activated 100% CS shows minimal initial exothermic activity until 3.5 h, when a single intense peak appears, representing delayed dissolution and subsequent polycondensation. X-ray diffraction (XRD) data indicate that the main crystalline phases of CS and EAFSS are stable in these alkaline systems; it is the glassy components that react. The use of CS and EAFSS in blended AAMs causes a minor increase in porosity of ~ 1–3% with respect to GGBFS only, and a small reduction in compressive and flexural strengths, although these reach 80 MPa and 8 MPa, respectively, after 28 days, even at a replacement level over 65 wt. %. Conversely, the 100% CS mixture exhibits a one-day compressive strength of 23 MPa, with a negligible increase thereafter. This result agrees with both FTIR and SEM analysis which highlight only minor changes in binder development after two days. It is believed that the unusual behaviour of CS in the investigated mixtures is related to the low availability of calcium in this precursor material.

Interlocking Bricks: Density and Compressive Strength Reduction Due to Addition of Kaolin Clay and RHA

This study investigates the density and compressive strength of interlocking bricks made of mortar added with kaolin clay as cement replacement and RHA for sand replacement. This research also investigated the chemical composition of kaolin clay and RHA used for the interlocking bricks. The mortar used was designed based on the concrete mix proportion of 1:2:3 but removed the coarse aggregate. The water-to-cement ratio utilized was 0.6. Each design mix comprises a combination of kaolin clay and RHA at 5%, 10% and 15% by the total weight of cement and sand, respectively. This paper demonstrates the chemical elements of the kaolin clay and RHA and reports the density and compressive strength of the interlocking bricks comparedto control samples. The results indicate that the density and compressive strength of the interlocking bricks decreases as the percentage of kaolin clay and RHA increases. The design mix containing 5% kaolin clay and RHA showed the highest density and compressive strength at 28 days, but the values were smaller than the control mix.In comparison to the control mix, the finding is as follows. At 28 days, the range of density reduction from day 3 for all mixes is between 16 to 25%. Meanwhile, the compressive strength of all mixes decreased by more than 65%, measured in the same duration. The result also showed that silicon dioxide (SiO2) contributes the most significant chemical element in kaolin clay and RHA. Kaolin clay contains almost 65% of SiO2, while RHA holds more than 90% of SiO2.

Enhancing the mechanical performance of notched glass/epoxy composite laminates via hybridisation with thermoplastic fibres

This study examines empirically and theoretically the open-hole tension and compression characteristics of thermoset composites using hybrid glass/polypropylene and glass/innegra yarns. The Abaqus software, finite element analysis (FEA) has been adopted to predict the tensile and compressive failure loads and damage failure modes for un- and notched samples under tensile and compressive strength tests. The commingling technique was used to create hybrid yarns, which were then transformed into non-crimp preforms before the infusion procedure. It was noticed that the inclusion of thermoplastic polypropylene (PP) and innegra fibres increased the ductility of yarns and composites. Densities of hybrid composites were also reduced by up to 20% when compared to pure glass/epoxy composites. Tensile and open-hole tensile (OHT) test results revealed that hybrid composites are less notch sensitive than glass/epoxy composites due to enhanced composite ductility. For glass composites, having holes resulted in a 41% decrease in tensile strength, compared to reductions of only 25% and 26% for PP and innegra fibre composites, respectively. Further, compression and open-hole compression (OHC) tests presented similar results with OHT tests whilst compressive strength reduction was lower for hybrid composites (10% and 11%) compared to glass/epoxy (28%) ones. The results of the numerical simulation for damage failure modes and tensile and compressive failure loads for un-notch and notched composite laminates are consistent with the experimental findings both qualitatively and quantitatively.

Development of low-carbon and cost-effective ultra-high performance concrete using carbonated recycled fine aggregate

This paper studied the influence of carbonated recycled fine aggregate (RFA) on mechanical and microstructural performance of ultra-high performance concrete (UHPC), aiming to develop a low-carbon and cost-effective UHPC. This includes the changes in strength, hydration kinetics, RFA-to-paste interfacial microstructure, and pore structure with the use of carbonated RFA. The environmental and economic effect of using carbonated RFA in UHPC is evaluated. The RFA content was investigated at 0–30%, by mass of total sand. Experimental results showed that a reduction greater than 10% in crushing index and water absorption of RFA was achieved by carbonation. The increase of carbonated RFA content from 0 to 30% led to 45% reduction in autogenous shrinkage of UHPC. The use of 20% uncarbonated RFA resulted in 12% and 10% reduction in 28-d compressive and flexural strengths, respectively, while such use of carbonated RFA can secure similar 28-d compressive and flexural strengths compared to those without RFA. Despite the reduced cement hydration, the use of carbonated RFA can secure a denser RFA-to-paste interfacial microstructure and refine the pore structure of UHPC compared to those made with uncarbonated RFA, given the chemical bonding and nucleation effect of carbonated RFA. Moreover, the use of 20% carbonated RFA can enable 5% decrease in the Global Warming Potential value evaluated by life cycle assessment compared to that without RFA. Such use of RFA led to a decrease greater than 15% in UHPC cost. This indicated the low-carbon and cost-effective characteristics of the developed UHPC made with carbonated RFA.