Structural Lightweight Aggregate Concrete Research Articles

Biochar-enabled carbon negative aggregate designed by core-shell structure: A novel biochar utilizing method in concrete

Using carbon-negative biochar is promising for the carbon footprints reduction of construction materials; however, directly utilizing biochar in concrete would negatively influence its mechanical properties, particularly when the utilizing volume exceeds a certain threshold. By designing as a core-shell structure through cold-bonding method, a novel carbon-negative core-shell aggregate (CSA) with a biochar core and a cementitious shell was developed in this study. The aggregate was characterized by strength, density, and water absorption measurements, meanwhile, analyzed by hydration heat, XRD, TGA, SEM/BSE, and X-CT. The results showed that the developed MG80 biochar-CSA attained a loose bulk density of 789 kg/m3. It exhibited a crushing strength of 6.84 MPa, a water absorption value of 19.4 %, and a significantly superior strength efficiency of 8669 Pa·m3/kg compared to commercially sintered artificial lightweight aggregates and other cold-bonded aggregates documented in literature. The carbon emission assessment indicated that producing one ton of MG80 biochar-CSA emitted −69 kg CO2, which was much lower than the commercial sintered aggregates. Concrete developed by replacing natural aggregate with 90 % MG80 biochar-CSA exhibited a compressive strength of 42.2 MPa while maintaining lightweight with density of 1866 kg/m3, which conforms to the standard-classified structural lightweight aggregate concrete.

Bending performance of lightweight aggregate concrete beam subjected to reinforcement corrosion: Experimental and numerical study

The application of lightweight aggregate concrete (LWAC) benefits the structural behavior of long-span and high-rise buildings. However, the corrosion-related durability issue of bending elements made of LWAC has remained unresolved for decades, and the bending performance of corroded LWAC beam, including load-bearing capacity, stiffness, cracking, and etc., has not yet been clearly defined due to limited knowledge in the available literature. This study aims to investigate the bending performance of LWAC beams subjected to reinforcement corrosion, and the test results provide valuable data for addressing the research gap relevant to the topic and contribute fundamental knowledge to the promotion of structural LWAC elements. Seven reinforced LWAC beams were tested to examine the cracking behavior, characteristic loads and deflections, deformation ability, and distribution of cross section strain at various moments. The modelling method considering the effect of rebar corrosion for LWAC beam was proposed. It was concluded that the corrosion of longitudinal rebar led to decreased cracking, yielding, and ultimate moment of LWAC beam, while the corrosion of stirrups increased the cracking moment and had little effects on the yielding and ultimate moments. The ductility of the tested specimens initially decreased and then increased with the raising corrosion level of the longitudinal rebar, which was attributed to the variation in bond performance between the rebar and LWAC. All tested beams exhibited a yielding deflection smaller than 1/235 of the span length. The strain distribution of the mid-span cross-section exhibited a nonlinear feature with increasing mass loss of the corroded longitudinal steel rebar. The proposed modelling procedure considering the corrosion effect showed good agreement with the test results, and a preliminary analysis of the bending performance of LWAC beams with different steel reinforcement corrosion ratios was completed. Data Availability StatementAll data, models, or code that support the findings of this study are available from the corresponding author upon reasonable request.

Enhancement of Perlite Concrete Properties containing Sustainable Materials by Incorporation of Hybrid Fibers

Utilizing waste resources in concrete manufacturing, while employing alternative components and minimizing the Ordinary Portland Cement (OPC) production, is a matter of great importance owing to several environmental and stability considerations. OPC is the fundamental component implemented in the conventional concrete production process. However, the OPC industry has raised environmental concerns since it produces mass amounts of carbon dioxide (CO2). A more sustainable substance, utilizing metakaolin as pozzolanic material and local ash as a filler can serve as an OPC substitute, thereby reducing the CO2 release into the environment. This work examines the impact of incorporating sustainable recycled copper fibers as well as alkali resistance glass fibers on the properties of perlite structural lightweight aggregate concrete containing local, sustainable materials. The research includes slump, density, and thermal conductivity tests along with tests conducted during the 7, 28, and 60 days of curing for compressive, flexural, and split tensile strength. The concrete was reinforced with 1% hybrid fibers by volume. The results reveal that adding fibers to lightweight concrete reduces the slump and increases density and thermal conductivity, while it also increases the compressive, flexural, and split tensile strengths.

Impact of fine lightweight aggregates and coal waste on structural lightweight concrete: Experimental study and gene expression programming

Light Expanded Clay Aggregate (LECA) is one of the materials used to make lightweight concrete. In this study, two types of lightweight aggregates including LECA in both coarse and fine aggregate forms and pumice in fine aggregate form have been used to produce lightweight aggregate concrete. Coal waste is also used as partial replacement for cement. The results show that the usage of pumice as partial replacement for sand and LECA as coarse aggregate is applicable and can used for producing structural lightweight aggregate concrete. Furthermore, by using and increasing in the amount of LECA as fine aggregate, the slump of lightweight concrete in comparison to using sand, is also increased. The mixtures with LECA in both fine and coarse aggregate forms have the best results. Also, the results show that adding the coal waste improves the properties of lightweight concrete, and the optimal ratio is about 15% as partial replacement for cement by weight. In addition, gene expression programming is employed to establish empirical connections derived from experimental outcomes. In this regard, a relationship is proposed to determine the compressive strength of lightweight aggregate concrete based on the experimental data. The outcomes of gene expression programming demonstrate that the suggested formula exhibits good accuracy and efficiency in forecasting the specified parameter.

Recycling of Oil Palm Shell as Aggregate in Concrete: A Review

The consideration of using alternative materials as coarse aggregates in construction industry is to conserve the natural resources, reduce undesirable carbon dioxide (CO2) and environmental degradation related to conventional aggregate. Oil palm shell (OPS) which is a by-product from oil palm industry has shown potentials as an alternative to the conventional aggregate in concrete production. This paper reviews the previous studies on the application of OPS as a construction material and has been extensively used in tropical countries. The performance of OPS meets the minimum requirements for lightweight aggregates. It is suitable material for the production of structural lightweight aggregate concrete with 28-day compressive strength more than 25 MPa. The various improvement techniques employed OPS concrete that resulted in improved OPS concrete performance are also highlighted in this review.

Lightweight cementitious composites incorporating fly ash cenospheres and perlite microspheres

The research on lightweight concrete has been an area of interest, especially in modular construction since low self-weight can ease the transportation process and speed up construction time. Past research found that conventional lightweight aggregate concrete (LWAC) developed using coarse lightweight aggregates and natural fine aggregates can fulfil the requirement of structural lightweight concrete. However, the dry densities achieved by these LWAC are relatively high, at around 1750–2070 kg/m3. To address this issue while producing structural LWAC with a lower density range, micro lightweight aggregates (MLWA) with closed pore structures are utilized. In this study, two types of MLWA: fly ash cenospheres (FAC) and perlite microspheres (PM) were used to produce two series of lightweight cementitious composite (LCC). The incorporation level of MLWA was 25%, 50%, 75% and 100% by volume of coarse silica sand which was utilized to optimize the content of MLWA. The performance of LCC was investigated through compressive strength, flexural strength, water absorption, drying shrinkage and thermal conductivity tests. Use of FAC and PM yielded satisfactory compressive strength of up to 46.7 MPa and 45.3 MPa respectively at low densities. While flexural strength of mixes with FAC and PM reached 8.0 MPa and 8.7 MPa respectively. Use of 75% FAC showed the lowest water absorption of 3.3%. Incorporation of 100% PM reduced thermal conductivity by as much as 82.4%. The optimum LCC mix in this study comprised 75% FAC and 25% coarse silica sand which achieved a specific strength of 29.0 kPa/kgm−3 and a dry density of 1406 kg/m3, while having an average compressive strength and flexural strength of 40.8 MPa and 6.3 MPa at 28 days, respectively. The overall results show that LCC made up of FAC is more suitable for structural applications, whereas LCC made up of PM exhibits better thermal insulation properties.

Thermal Performance Assessment of Lightweight Aggregate Concrete by Different Test Methods

Structural lightweight aggregate concrete is currently an alternative to normal-weight concrete when thermal insulation properties are required to meet the objectives of energy efficiency and sustainability. The accurate evaluation of the thermal performance is thus essential for designing structural lightweight concrete elements. This paper aims to evaluate the thermal behavior of structural lightweight aggregate concrete, assessed through different tests methods. To this end, a vast experimental campaign was carried out involving specimens produced with several types of lightweight aggregate and different water/cement ratios. The thermal performance was established by thermal conductivity, which was determined according to a modified transient pulse method and a quasi-stationary method, and specific heat capacity, which was determined through a transient pulse method and a heat transfer method. Normal-weight concrete was also tested for comparison purposes. Experimental evidence showed that lightweight aggregate concretes with lower density are associated with up to about 50% lower thermal conductivity and higher specific heat capacity than normal-weight concrete. Moreover, the study demonstrated that the expeditious transient pulse method is suitable for assessing the thermal conductivity of this type of concrete, and that both the transient pulse method and the heat transfer method are adequate to determine the specific heat capacity.

Effect of Moisture Condition of Structural Lightweight Concretes on Specified Values of Static and Dynamic Modulus of Elasticity.

The dynamic modulus of elasticity (Ed), specified by ultrasonic pulse velocity measurements, is often used, especially for concrete built into construction, to estimate the static modulus of elasticity (Ec,s). However, the most commonly used Equations for such estimations do not take into account the influence of concrete moisture. The aim of this paper was to establish this influence for two series of structural lightweight aggregate concrete (LWAC) varying in their strength (40.2 and 54.3 MPa) and density (1690 and 1780 kg/m3). The effect of LWAC moisture content turned out to be much more pronounced in the case of dynamic modulus measurements than for static ones. The achieved results indicate that the moisture content of the concrete should be taken into consideration in modulus measurements as well as in Equations estimating Ec,s on the basis of Ed specified by the ultrasonic pulse velocity method. The static modulus of LWACs was lower on average by 11 and 24% in relation to dynamic modulus, respectively when measured in air-dried and water-saturated conditions. The influence of LWAC moisture content on the relationship between specified static and dynamic moduli was not affected by the type of tested lightweight concrete.

Mechanical and Microstructure Properties of Plain and Blended Cement Structural Lightweight Aggregate Concrete Using Sintered Fly Ash Aggregates

Infrastructure and industry have grown dramatically as a result of globalization and urbanization. However, there are certain challenges, such as meeting infrastructural needs that require a large amount of extraction of natural aggregates and disposal of waste generated as a result of industrialization. Both of these challenges have an adverse impact on the environment. Deforestation, erosion, contamination of nearby streams, and increase in noise, dust, and emissions are all consequences of aggregate extraction. The industrial waste can contaminate groundwater, lakes, streams, rivers and coastal waterways and harm the land and neighboring water bodies. Hence these challenges must be addressed as a priority for environmental sustainability. The current study developed structural lightweight aggregate concrete (SLWAC) using sintered fly ash aggregate (SFA). The investigation was done with the use of different binders such as Portland Pozzolana Cement (PPC), Ordinary Portland Cement (OPC), and Micro Fibre Cement (MFC). The present study explores the suitable binder to produce SLWAC at different water-cement ratios of 0.4, a0.44, and 0.48. The performance evaluation of SLWAC was investigated by mechanical behavior like compressive strength, split tensile, flexural strength, and impact test. Microstructure analysis is also included in this study to validate the mechanical experiment results. SLWAC made from OPC shows more mechanical strength than PPC and MFC, due to faster hydration and early strength gain. SLWAC made from microfiber cement, has more strength as compared to PPC. This could be due to fibers in MFC, acting as a reinforcing agent, which reduces micro cracks. The microstructure of SLWAC shows that the wall effect does not exist in SLWAC compared to normal aggregate concrete. It has a uniform and continuous microstructure of hydration products and partially penetrates the SFA. It could be associated with the superior interfacial transition zone having a lower w/c ratio because of the higher absorption of SFA. The findings show that all developed SLWAC can be used in structural members like beams, columns, and slabs.

Experimental Study on Utilizing Polyethylene Terephthalate Waste as a Substitute for Coarse Aggregate in the Production of Lightweight Concrete

Concrete is a building material that consists of a mixture of aggregate and paste. Normal concrete has a unit weight of 2200 kg/m3 to 2500 kg/m3. In addition to normal concrete, lightweight concrete is also known which has a unit weight of less than 1900 kg/m3. The research was conducted to produce lightweight concrete by using aggregate from polyethylene terephthalate (PET) plastic waste as a substitute for coarse aggregate. This study used 40 cylindrical samples of 150 mm x 300 mm with variations in the use of PET aggregates of 25%, 50%, and 100% of the volume of coarse aggregate. The results show that the use of PET aggregates produces concrete with a decrease in compressive strength of 26%–39% and a decrease in water absorption of 2%–32% from normal concrete. Ultrasonic Pulse Velocity (UPV) testing showed that the concrete with PET aggregates had a lower wave propagation velocity compared to normal concrete. Moreover, Schmidt hammer and splitting tensile test showed that concrete with PET aggregates had lower rebound number and split tensile strength compared to normal concrete. PET substitution percentages of 25% and 50% resulted in unit weights of 2218 kg/m3 and 2102 kg/m3, respectively, which rule out the use of lightweight concrete. However, 100% PET substitution has a unit weight of 1855 kg/m3 with a compressive strength of 14.16 MPa, which can be categorized as moderate structural lightweight aggregate concrete.

Assessment of the engineering properties and economic advantage of recycled aggregate concrete developed from waste clay bricks and coconut shells

Using recycled aggregates to replace natural aggregates in concrete helps preserve nonrenewable resources, promotes recycling, and affords reductions in cost. To this end, experiments were performed to clarify the effects of coarse aggregate systems developed using crushed coconut shell aggregate (CCSA) and recycled brick aggregate (RBA) on the mechanical properties, thermal conductivity, ultrasonic pulse velocity and high temperature resistance of concrete. The results showed that the incorporation of CCSA improved the thermal conductivity, flexural strength and cost ratio of concrete. The mechanical properties of the recycled aggregate concrete also satisfied the requirements of structural lightweight aggregate concrete. In addition, low-rigidity concrete developed using RBA and CCSA imparted the building with a higher strain capacity, suitable for applications in seismic regions. However, under high-temperature environments, the properties of the concrete deteriorated significantly with the incorporation of CCSA; the compressive strength and other properties were also reduced considerably.

Machine Learning-Based Predictive Modeling of Sustainable Lightweight Aggregate Concrete

Nowadays, lightweight aggregate concrete is becoming more popular due to its versatile properties. It mainly helps to reduce the dead loads of the structure, which ultimately reduces design load requirements. The main challenge associated with lightweight aggregate concrete is finding an optimized mix per requirements. However, the conventional material design of this composite is quite costly, time-consuming, and iterative. This research proposes a simplified methodology for the mix designing of structural and non-structural lightweight aggregate concrete by incorporating machine learning. For this purpose, five distinct machine learning algorithms, support vector machine (SVM), artificial neural network (ANN), decision tree (DT), Gaussian process of regression (GPR), and extreme gradient boosting tree (XGBoost) algorithms, were investigated. For the training, testing, and validation process, a total of 420 data points were collected from 43 published journal articles. The performance of models was evaluated based on statistical performance indicators. Overall, 11 input parameters, including ingredients of the concrete mix and aggregate properties were entertained; the only output parameter was the compressive strength of lightweight concrete. The results revealed that the GPR model outperformed the remaining four machine learning models by attaining an R2 value of 0.99, RMSE of 1.34, MSE of 1.79, and MAE of 0.69. In a nutshell, these simplified modern techniques can be employed to make the design of lightweight aggregate concrete easy without extensive experimentation.

Mechanical properties and microstructure of ultra-high strength concrete with lightweight aggregate

In recent years, the development of concrete has been toward to the direction of lightweight and high strengthening. This study developed a kind of lightweight ultra-high strength concrete(L-UHSC) through the comprehensive design method, which had an apparent density rang of 1995 kg/m3-2114 kg/m3 and a compressive strength of 102.4–114.5 MPa. The specific strength of the designed L-UHSC is more than 50 MPa/(t/m3), which is higher than ordinary structural lightweight aggregate concrete (LAC). Additionally, the roles of high-performance paste, lightweight aggregate (LWA) and steel fiber in L-UHSC were revealed through scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and strength test. The findings revealed that SF content, rather than the binder-sand ratio and aggregate ratio, has a greater impact on density and strength, and the aggregate ratio having the least effect. As steel fiber content increases from 0.5 % to 2.0 %, compressive strength, flexural strength and splitting tensile strength of LAC increase by 44.3 %, 120 % and 151 %, respectively, which is higher than that of ultra-high performance (UHPC). The micromorphology and pore structure research suggested that the high-performance paste plays a keystone role in achieving the ultra-high strength, and LWAs mainly affected strength through improving pore structure. In addition, small size pre-wetted LWA is more conducive to concrete strength. Our preliminary results provide a reference for the research and development of lightweight ultra-high strength cement composites.

Mechanical properties of lightweight expanded clay aggregate (LECA) concrete

The construction activities are based on structural concrete, which is one of the most commonly used materials. The fundamental aim of using lightweight concrete (LWC) was to reduce the concrete self-weight of the structure parts. As a result, LWC has been used successfully in a variety of installations for several years. In this paper, the mechanical properties of concrete made with lightweight expanded clay aggregate (LECA) as a full replacement for coarse aggregate are studied. The experimental program shows that LECA with a 32 MPa cube compressive strength and an 1,823 kg×m–3 dry density can be used to make structural light-weight aggregate concrete (SLWC). The results show that the reduction in the strength of lightweight aggregate concrete (LWAC) was found to be higher in the concrete with an estimated compressive strength of 32 MPa due to the lower strength of the LWA (expanded clay). According to the test results, the mechanical properties of LWC were greatly improved by adding silica fume (SF). Furthermore, LECA concrete has a splitting tensile strength that is 47% higher than the ASTM C330/C330M-17A minimum requirement. The LECA concrete has a splitting tensile strength to compressive strength ratio of approximately 13%. Additionally, the results demonstrate a 27% difference in the modulus of elasticity between the calculated and tested values.

Thermo-mechanical efficiency of fibre-reinforced structural lightweight aggregate concrete

The construction industry must consider not only the mechanical performances of structural materials but also their thermal performances for energy-efficient buildings. There exist conflicting thermal and mechanical properties between normal weight concrete (NWC) and lightweight aggregate concrete (LWAC). NWC with high mechanical strength exhibits poor thermal efficiency but LWAC possesses low mechanical strengths but high thermal efficiency. The inclusion of fibres in the mixture of LWAC could provide a solution to its weaknesses in mechanical properties however its thermal performance was not well fully understood. To produce an energy-efficient building material, this study was conducted to determine thermo-mechanical performances of steel (ST) and polypropylene (PP) fibre-reinforced LWACs that meet the structural code requirements with good thermal properties. Lightweight expanded clay aggregate was used to make a structural LWAC and polypropylene and steel fibres were used as the reinforcement. Test results revealed that structural LWAC reinforced ST fibre with 1.0% dosage has the best mechanical and thermo-mechanical efficiency whilst PP fibre with 0.3% dosage has the best thermal performance.The ST fibre has a positive influence on the compressive and tensile strength than PP fibre. In terms of overall thermal performance and cost, LWAC containing 0.3% PP fibre was the most desirable. The PP fibre has a more positive influence on thermal properties than ST fibre. The equations had been proposed with a good correlation of R2 > 0.7979 to predict the thermal properties against density for ST and PP fibres. The new merit Mo equation provides a novel way to measure the thermo-mechanical efficiency of the building materials for the construction industry. ST fibre is better than PP fibre in enhancing the mechanical efficiency but PP fibre is more efficient than ST in enhancing the thermal efficiency of fibre-reinforced LWAC.

Influence of Different Ambient Temperatures on the Thermal Properties of Fiber-Reinforced Structural Lightweight Aggregate Concrete

This study reports the influence of different climatic ambient temperatures on the thermal properties of fiber-reinforced lightweight aggregate concrete (LWAC). Lightweight expanded clay aggregates (LECA) with steel (ST) and polypropylene fibers were used in the mix proportions. The steady-state thermal test was performed on concrete samples at the oven-dry state with the measurement taken at six different climatic ambient temperatures of 0 °C, 10 °C, 20 °C, 30 °C, 40 °C, and 50 °C. The results show a linear dependence of thermal conductivity, specific heat, thermal diffusivity and thermal effusivity of fiber-reinforced LWACs against the different ambient temperatures. These ambient temperature variations are discussed as a function of the thermal properties of fiber-reinforced LWAC. The thermal conductivity and thermal diffusivity decrease linearly between 0 °C and 50 °C, whilst the specific heat and thermal effusivity increase linearly between 0 °C and 50 °C. Equations with strong correlations to predict thermal properties of fiber-reinforced LWAC were proposed based on the results of this study. The significance of this research is to propose the dynamic ambient temperature-dependent thermal properties equations that can be used in the energy analysis of the buildings.

Mechanical properties and freeze-thaw resistance of lightweight aggregate concrete using artificial clay aggregate

Abstract This work intends to make structural lightweight aggregate concrete by using artificial expanded clay aggregate with different replacement levels from normal coarse aggregate and improve it with a high-performance superplasticizer to increase its strength. The mechanical characteristics covered in the present work were compressive strength, flexural strength, and splitting tensile strength in addition to freezing and thawing resistance. Different densities were found for all mixes ranging between normal and lightweight concrete and that depends on the replacement of normal aggregate with lightweight aggregates. Mixes with replacement exceeding 25% give compressive strength less than 17 MPa and cannot be regarded as structural lightweight concrete. Modified mixes give higher values of mechanical properties, and also some non-structural lightweight concrete mixes were improved to structural lightweight concrete by using PC-superplasticizer in this study. The research also includes freezing and thawing cycles on reference mixes and lightweight mixes. Lightweight mixes give high durability against freeze-thaw cycles where the reduction in compressive strength was 6.2, 4.6, and 5.5% for 10% rep, 15% rep, and 20% rep mixes, respectively, compared with 32.2% reduction for reference mix.

Size effect on tensile strength of lightweight aggregate concrete: A numerical investigation

Lightweight aggregate concrete (LWAC) showed an obvious brittleness when subjected to the tensile stress, and the related size effect issue was crucial for the analysis and design of structural LWAC. The random aggregate structure was used to establish finite element models, and materials parameters were calibrated by using existing test data. Influences of the ratio of water-to-binder (W/B) materials, grading of lightweight aggregate (LWA), the strength of LWA and the relative strength of interfacial transitional zone on the tensile strength and the size effect of LWAC were evaluated. Finally, the results of simulations were applied to conduct a regression analysis on classical size effect law. It was concluded that the grading of LWA had a relatively more minor influence on the size effect of LWAC in tension, while the W/B ratio and the strength of LWA significantly affected the size effect due to the alteration of the concrete strength. Formulas for parameters in classical size effect law were developed by using the results of numerical analysis.

Thermal and acoustic properties of sustainable structural lightweight aggregate rubberized concrete

This study investigated the effect crumb rubber recycled from wasted tires on properties of structural lightweight aggregate concrete (LWAC). Two types of concrete were tested: control LWAC and rubberized lightweight aggregate concrete (RLWAC). The control LWAC consisted of cement, fine aggregate (river sand), and lightweight coarse aggregate (porous aggregates). For the RLWAC, the fine aggregate was replaced by crumb rubber at the rate of 10, 20, 30, 40, and 50% by volume. The water to cement ratio for both concrete types was set at 0.35. The experiment series consisted of density (ASTM C567), compressive strength (ASTM C39), flexural strength (ASTM C78), thermal conductivity (ASTM C518), and sound absorption coefficient (ISO 10534-2). Results showed the decrease in density of about 10%, compressive strength of 21.4%, and flexural strength of 35.4% with the increasing crumb rubber replacement ratio up to 50%. For thermal and sound properties, the increasing crumb rubber content of up to 50% improved the thermal insulation of concrete, as seen by the decrease in thermal conductivity by about 14.6%. RLWAC also exhibited superior sound insulating properties to LWAC as seen by higher sound absorption coefficient over the working sound frequency range. In order to satisfy the requirements of ASTM C330 and ACI 318, the optimum crumb rubber replacement was recommended at less than 10%.

Meso-scale stochastic modeling for mechanical properties of structural lightweight aggregate concrete

Meso-scale stochastic modeling for mechanical properties of structural lightweight aggregate concrete