Natural Lightweight Aggregate Research Articles

The impact of slag on the process of geopolymerization and the mechanical performance of mine-tailings-based alkali-activated lightweight aggregates

Alkali-activated lightweight aggregates (LWAs) made of alkali-activated aluminosilicate-rich mine tailings (MTs) offer a promising alternative to natural lightweight aggregates. The comprehensive investigation of lightweight aggregate production using aluminosilicate-rich MTs in combination with commercial slag as a reactive aluminosilicate remains largely unexplored. In this study, mixtures of MTs and slag were pelletized through the application of a pan pelletizer machine. The study focused on examining the impact of different slag concentrations on the chemical, physical, mechanical, mineralogical, and morphological properties of the produced LWAs. Furthermore, a comparison was made between the physical and mechanical characteristics of the resulting LWAs and those of flay-ash (FA)-based LWAs. The results revealed that the inclusion of slag in LWAs, as compared to FA, led to the production of LWAs with superior physical and mechanical properties. Specifically, as the slag content increases, the water absorption, dissolution, and porosity of LWAs significantly decreased, while the bulk density and compressive strength increased. It is important to note that these changes occur without affecting the specific gravity of the LWAs. The scanning electron microscope (SEM) images clearly showed that the addition of slag, similar to FA, especially at concentrations of more than 20% and higher, promoted uniform geopolymerization within the specimens. Furthermore, the energy-dispersive X-ray spectroscopy (EDS) analysis revealed that all LWAs with concentrations of 20% slag and higher exhibited a Si:Al ratio exceeding three, indicating a higher likelihood of geopolymer backbone formation. The X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) analyses revealed that the alkali activation process led to the depletion of gypsum, originally present in the MTs, and the emergence of sodalite and zeolite in the LWAs. Thermogravimetric analysis (TGA) tests provided additional confirmation of the ongoing geopolymerization process in slag-based LWAs, particularly those containing 20% slag or higher.

The effect of class F fly ash on the geopolymerization and compressive strength of lightweight aggregates made from alkali-activated mine tailings

Lightweight aggregates (LWAs) produced using alkaline activation of aluminosilicate-rich mine tailings (MTs) are viable substitutes for natural lightweight aggregates used in construction and building industry. However, most pure MTs do not contain adequate quantities of amorphous aluminosilicates to make geopolymerization feasible without adjusting the Si:Al ratio through the incorporation of amorphous aluminosilicates or other aluminum/silicon source materials. A comprehensive exploration of the production of LWAs using MTs in conjunction with reactive aluminosilicates has not yet been thoroughly investigated. In this study, class F fly ash (FA) was used as an amorphous supplement to adjust the Si:Al ratio, leading to improved geopolymerization of LWAs. The mixtures of MTs and FA were pelletized using a disk granulator machine by spraying 10 M NaOH with a liquid-to-solid ratio (L/S) of 0.25. The effects of different concentrations of FA (10%, 15%, 20%, 25%, and 30%) on the chemical, physical, mechanical, mineralogical, and morphological features of the resulting LWAs were examined. The results indicate that increasing the FA content of LWAs decreased their water absorption and porosity while increasing their bulk density and compressive strength without affecting their specific gravity. The scanning electron microscope (SEM-EDS) images show that by increasing the FA content, especially at 20% and upward, homogeneous geopolymerization was achieved in the specimens and the Si:Al ratio in LWAs with 20% or more FA was greater than three, indicating a greater likelihood of geopolymer backbone formation. The results of x-ray diffraction spectrometry (XRD) and Fourier-transform infrared spectroscopy (FTIR) showed that the alkali activation process resulted in the disappearance of the gypsum phase originally available in the MTs and the appearance of sodalite (sodium carbonate) in the LWAs. Future research should utilize the Life Cycle Assessment (LCA) methodology to evaluate environmental impact and should explore advanced additives/modifiers for improved mechanical characteristics and manufacturability to increase potential construction applications.

Green lightweight concrete utilizing sustainable processed recycled plastic aggregates: Technical, economic and environmental assessment

In recent years, it has become imperative to conduct studies on the environmental effect of the construction industry on sustainability and develop strategies to mitigate sustainability risks. These mitigation strategies aim to protect natural resources and reduce waste accumulation. The life cycle analysis of buildings has been one of these studies due to the adverse environmental effects of the materials utilized in construction, particularly concrete. Specifically, how material use affects global warming and consumer desires for energy-efficient and environmentally friendly buildings. This study presents a comprehensive life cycle assessment of operational and embedded energy components that affect overall energy consumptions for concrete construction. Five concrete mixtures with varying percentages of sustainable recycled plastic aggregate were compared to a control mixtures made with normal weight and natural lightweight aggregates using a case study of a two-story residential building in Saudi Arabia. A life cycle assessment was initially used to estimate the embodied impact of producing the concrete. Then operational energy use was simulated using IES-VE. The weathering profile, transportation distance, and processing energy were all considered and calculated using site-based data for the environmental impact assessment components. The results demonstrate significant reduction of annual operational energy, carbon emissions and overall energy consumption of up to 15%, 13% and 21%, respectively. Therefore, the resulting green concrete system is more environmentally friendly due to the superior thermal performance over existing natural lightweight aggregates concrete. This evidence enables the ideas to be implemented, particularly in dry climate countries such as Saudi Arabia, where the average electricity use is very huge. Additionally, the study results suggest the possibility of permanently integrating plastic wastes into sustainable aggregate and its subsequent green concrete to reduce these wastes' adverse effects.

Life cycle sustainable assessment of natural vs artificial lightweight aggregates

Optimal selection of concrete aggregates can promote sustainable construction practice from the bottom line, which is a feasible strategy to cope with resources crisis and solid waste pollution. In this study, a two-level tree structure framework was thus proposed for the sustainability assessment of lightweight aggregates (LWA) based on the life cycle assessment concept. The evaluation system was divided into four criteria categories marked as society demands, economic costs, environmental impacts and technical performance, and each of them was assigned a number of sub-index. A qualitative questionnaire survey with seven sub-index and a quantitative calculation with eight sub-index were executed in the target system. Sintering fly ash aggregates (SFFAA), cold-bonding fly ash aggregates (CBFAA), waste clay brick aggregates (WCBA) and natural pumice aggregates (NPA) were chosen as typical artificial and natural lightweight aggregates objectives and evaluated in the framework. Impact and sensitivity analyses were conducted to comparably discuss the sustainability of various lightweight aggregates. The impact analyses represented that the waste clay brick aggregate has better sustainability. The sensitivity analysis shows that the supply-demand relationship of raw materials greatly impacts the sustainability of lightweight aggregate, and the transportation distance of raw materials is the critical factor in the production of LWA. At the same time, artificial lightweight aggregates are sensitive to cement binder consumption, and zero cement addition or waste cement powder is an optimistic option. From the sustainable life cycle assessment results, waste clay brick aggregates, sintering fly ash aggregates and cold-bonding fly ash aggregates are suggested as the alternative to the natural pumice aggregates for the lightweight aggregates concrete production. The emphasis on the weight of the social dimension will tend to prefer the selection of SFAA, and the economic or environmental dimension will lead to the preference of CBFAA for sustainable development. The framework proposed in this work could be used in choosing other sustainable construction materials or cleaner products.

Flexural performance and ductility of RC beams made using natural LWA

This paper evaluates experimentally the feasibility of utilizing local natural lightweight aggregates (LWA) for designing reinforced concrete (RC) beams. The aggregates investigated were of scoria origin, with an absorption capacity of 10%, and dry densities ranging between 860 and 1120 kg/m3. A series of full-scale 16 simply supported RC beams of rectangular cross section were designed using two concrete strengths, normal and high, and two tension steel ratios of the balanced reinforcement ratio, following ACI code requirements. For the lightweight concrete (LWC) mixes designed, the replacement level of normal weight aggregates (NWA) with coarse LWA was 100%, whereas the replacement level for fine LWA was 62.5%. Data presented include load-deflection, and moment-curvature graphs, cracking behavior, mode of failure and ductility indexes. Test results indicated that the flexural response of LWC beams was similar to that of normal weight concrete (NWC) beams. All the LWC beams tested failed in ductile flexural mode, exhibited relatively larger mid span deflections, higher curvatures, and wider cracks, compared to NWC beams of equal concrete strength and steel ratio. The most influential parameter on the ductility indexes of LWC beams was the steel ratio. Moreover, the scoria LWA investigated can be used successfully in structural design.

Predictive study on Mechanical strength of Lightweight concrete using MRA and ANN

The lightweight concrete is preferred over regular density concrete as it which reduces the dead load of the structure due to its lower density. The reduction in dead load of the structure, resulting in a considerable decrease in the size of structural elements and reinforcements; thereby, the building's cost can be reduced. The lightweight concrete is achieved through natural lightweight aggregates, artificial lightweight aggregates, coconut shells, oil palm shells, aeration in concrete, etc. The mechanical properties like compressive strength, tensile strength, density depend upon lightweight aggregate, fine aggregate, super-plasticizer, cement content, water-cement ratio, etc. The mechanical properties can also be predicted using artificial intelligence from the existing data. This research aims to predict lightweight concrete's mechanical properties using MRA and ANN accurately.

Synthesis and characterization of lightweight aggregates through geopolymerization and microwave irradiation curing

This work is designed with the aim of synthesis of lightweight aggregate (LWA) by geopolymerization. Fly ash (FA) and silica fume (SF) are used as precursors (alumino-silicate constituents), which are activated with the combination of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3). Two types of LWAs; foam (FLWA) and solid (GLWA), are formulated by varying the constituents, all pellets are handcrafted and cured in microwave irradiations for 5 min. Morphology and physico-mechancial performance for both types are evaluated and relationship among them are also established. The morphological characteristics reveal that surface texture for both types are smooth and shape is spherical/rounded. However, FLWA has irregular shape due to non-uniform expansion (more than 30%) and also resulted in significant weight loss after expansion. The density of FLWAs gradually decreases due to the addition of Na2SiO3 (foaming agent), however, for both types the value is below ASTM limits (880 kg/m3). FLWAs are more porous and lighter than GLWAs and previously produced synthetic LWAs, while their properties similar with natural LWAs. The particle crushing strength for FLWA is almost 4.5 times less as compared to GLWA, due to such porous nature. Moreover, significant relationships among physico-mechancial properties have been established. Developed LWAs can guarantee required material property and have a great potential to be used as green construction material.

Mechanical properties and durability of high-performance concrete internally cured using lightweight aggregates

An experimental investigation was conducted to determine the effect of internal curing of natural lightweight aggregates (LWAs) on the shrinkage, mechanical properties, and durability of high-performance concrete (HPC). Conventional aggregates were partially substituted with prewetted coarse and fine LWA at dosages of 5, 10, and 20% by volume. The early age autogenous shrinkage and drying shrinkage of the HPC mixtures were monitored for up to 180 days. The investigated properties of the HPC mixtures included compressive strength, modulus of elasticity, and splitting tensile strength at 28 days, as well as rapid chloride permeability and water absorption. The results revealed that, at a replacement level of 20% for both coarse and fine aggregates, the reduction in autogenous shrinkage of the HPC mixtures was approximately 118% at 28 days and 65% at 18 days. Furthermore, the test results indicated that the autogenous shrinkage measured between 15 h and 7 days after casting was reduced by approximately 75%. Fine LWAs were more effective in reducing autogenous shrinkage than coarse LWAs. This was attributed to the small particles, which allowed a good distribution of the water-filled internal curing within the cement matrix. It was also found that using up to 20% LWA could modify the 28-day autogenous shrinkage of HPC by reducing the cube compressive strength up to 70 MPa as compared to 86 MPa for the control mixture. In addition, the obtained strength values of the concrete mixes were found to be within the acceptable range specified by the ACI standard to be categorized as HPC. The findings of the study revealed that the utilization of LWA is feasible as an internal curing method for decreasing the volume changes, particularly at the early ages, and for avoiding the formation of cracks in HPC.

Experimental study on lightweight concrete using pumice aggregate

Concrete is the commonly used manufactured building material in the world, owing to its usefulness and relatively low cost. One of the disadvantages of conventional concrete is its high self-weight. This heavy self-weight of concrete will result in uneconomical structural material. To decrease the self-weight of concrete, the coarse aggregate is replaced partially by lightweight aggregate. This is known as lightweight concrete having low density, reduction of dead load and to increase thermal insulation. There are two types of lightweight aggregate - natural lightweight aggregate and artificial lightweight aggregate. One of the most commonly available natural lightweight aggregate called pumice aggregate is used as a replacement for coarse aggregate. Pumice aggregate is used because of its low density than conventional coarse aggregate, and it is easily available. Lightweight concrete is prepared by partially replacing the coarse aggregate with pumice aggregate by 50%, 80% & 100%. The conventional concrete and pumice lightweight aggregate concrete is made by using mix M 30 with Conplast SP430 admixture. The mechanical and durability properties of conventional concrete and pumice lightweight aggregate concrete are compared by conducting various destructive and non-destructive tests and favorable replacement is found.

Life cycle assessment of lightweight concrete containing recycled plastics and fly ash

Researchers put significant effort to decrease the environmental impact of concrete by using industrial by-products as an alternative binder. However, the considerable environmental impact still exists due to the consumption of natural resources as aggregates. Natural aggregates are the most used resources by volume in the construction sector. Therefore, it is necessary to investigate by-products as an alternative to natural aggregates as well. This study presents the environmental impact of lightweight concrete (LWC) produced by replacing natural aggregates with recycled waste plastic (polyethylene) (RWP) and partially replacing Portland cement with Class F fly ash (FA). Life Cycle Assessment (LCA) was performed to compare a conventional LWC, containing pumice as natural aggregate and Portland cement as a binder, with green LWC, containing 30% RWP as pumice replacement and 20% FA as cement replacement. These scenarios were evaluated in terms of global warming potential, abiotic depletion, ozone layer depletion, terrestrial ecotoxicity, photochemical oxidation, acidification and eutrophication. LCA was coupled with mechanical tests at 7 days and 28 days. RWPs were found to be an environment-friendly replacement material for natural lightweight aggregates with an overall decrease in all CML-IA impacts except eutrophication. Tested green mix design also provided sufficient strength for nonstructural applications.

Investigating the effects of bacterial activity on compressive strength and durability of natural lightweight aggregate concrete reinforced with steel fibers

The present study investigated the effects of a specific strain of Bacillus subtilis introduced into natural lightweight aggregate concrete (LWAC) as a new approach on its water absorption, electrical resistance, compressive strength, chloride ion penetration, carbonation depth, water penetration depth, and compressive strength in a sulfate environment. For this purpose, specimens of two general groups were made: with and without bacteria. Two mix designs were also used to cast specimens with and without reinforcing steel fibers. The bacterial concentration in the concrete mix water was 107 cells.ml−1. Finally, the specimens were cured in the three different environments of plain water, urea-calcium lactate solution, and nutrient solution. Overall, 252 specimens were cast each with 2 replicates. Test results revealed that, compared to normal specimens, those containing bacteria in their mix water and cured in the calcium lactate environment, recorded decreases of about 13.1%, 20.5%, 27.2%, and 44.3%, respectively, in their water absorption, chloride penetration, carbonation depth, and water penetration depth while their electrical resistance increased by about 103.6%. Moreover, in this study additional specimens containing bacterial spores, due to their dormant state and sustainability in the alkaline environment of concrete, were also cast to compare the two types of specimens in terms of their water absorption, electrical resistance, and compressive strength. The results of this study showed that incorporating the bacterial treatment method in natural LWAC mixture reinforced with steel fibers reduces not only the high dead load and cracking potential of concrete elements but also their water absorption and chloride ion penetration due to the occlusion of fine cracks.

Effect of Lightweight Aggregates on early-age behavior of High Performance Concrete

Laboratory experiments were conducted to investigate the effects of locally available natural lightweight aggregates (LWA’s) on volume changes and mechanical properties of highperformance concrete (HPC). The normal aggregates fraction of high-performance concrete was replaced with fine and coarse LWA’s at three different replacement levels, 5%, 10% and 20% by volume. The test results indicated a significant reduction in the autogenous shrinkage of highperformance concrete at 56 days without a corresponding considerable reduction in compressive strength of the same concretes. The test results have also shown that up to 20% volume fraction of coarse LWA’s could be used for mitigating the volume changes of HPC with a slight reduction in compressive and splitting tensile strengths, and elastic modulus. Therefore, this investigation recommends the use of locally available natural LWA’s as a viable curing technique for minimizing the volume changes and risk of cracking of HPC’s without compromising their mechanical properties.

Acoustic insulation properties of lime mortars with natural lightweight aggregate

Porous pozzolan-active aggregate can be used to prepare lightweight lime mortars with high ability to salt accumulation from masonry, enhanced strengths and improved their acoustic and thermal insulation properties, or fire resistance. In this study, the effect of 3 types of natural lightweight aggregate on acoustic insulation properties of air lime mortars, NHL mortars, and cement-lime mortars has been investigated. Measurements of the signal attenuation in the frequency range of 16 Hz to 16 kHz showed the appreciable effect of binder and aggregate used in the mortars. Pumiceous aggregate caused the highest attenuation of the acoustic signal. The natural zeolite seems to be suitable aggregate to NHL and blended lime-cement plasters because it lightens the mortar and positively affects the acoustic attenuation.

Optimum Oil Palm Shell Content as Coarse Aggregate in Concrete Based on Mechanical and Durability Properties

Oil palm shell (OPS) is a biosolid waste in palm oil industry in the tropical countries which could be used as aggregate in concrete mixture. Since 1984, OPS has been experimented as natural lightweight aggregate in research studies to produce lightweight concrete (LWC). Medium and high-strength LWCs using OPS as coarse aggregate were successfully produced. However, higher drying shrinkage and lower mechanical properties for concretes containing higher volume of OPS are reported in previous studies. Therefore, OPS is not fit to be used as full coarse aggregate in concrete mixture and therefore, there should be an optimum OPS content in concrete. In this study, in a normal-weight concrete, normal coarse aggregate was replaced with OPS from zero to 100% with an interval of 20%. Tests such as slump, density, compressive strength in different curing conditions, splitting tensile strength, initial and final water absorptions, and drying shrinkage of cured and uncured specimens were conducted to find out optimum OPS content in concrete. From the test results, it could be summarized that OPS content should not exceed 60% of total volume of coarse aggregate.

Mechanical properties of lightweight aggregates concrete made with cameroonian volcanic scoria: Destructive and non-destructive characterization

This paper analyses the properties of concrete produced with Natural Lightweight Aggregates from Cameroonian volcanic scoria VS. Two groups of concretes with VS were prepared. A first concretes group produced with a natural sand from Covilhã-Portugal was cast in cubic specimens (150×150×150mm) and a second with a natural sand from Rabat-Morocco was cast in cylindrical specimens (160×320mm). The concrete mechanical properties were evaluated by non-destructive tests (NDT) and destructive test (DT). Schmidt Rebound Hammer (SRH) and Ultrasonic Pulse Velocity (UPV) were performed to determine the concrete rebound number (RN) and the concrete dynamic modulus of elasticity (Ed) at 28, 56 and 90 days. The concretes compressive strength at 28, 56 and 90 days on cylindrical specimens has been determined using DT method and predict by empiric expressions, normally applied for normal concretes, in function of RN or/and UPV. The results show that, at ages from 28 to 90 days, the concrete compressive strengths increase by 27.42–35.36%, the RN increase by 5.2–22.3%, while the UPV increase only by 4.2–7.4%.A concrete compressive strength model fc28 was proposed considering the effect of water-binder (W/B) and aggregate-binder A/B ratios, matrix volume Rm, VS aggregate VVSA and sand Vs, the densities of the aggregates and the characteristic resistance of the cement RC. It has been concluded that W/B, A/B, VVSA and RC showed more influence on the prediction model than Vm and Vs. Finally, it was concluded that concretes with VS from Cameroon can be used as structural or semi-lightweight concrete.

Bond behavior of steel bars embedded in concretes made with natural lightweight aggregates

The bond properties of reinforcing steel bars embedded in structural concrete made with locally available natural lightweight aggregates, was studied using pull-out tests on cubic specimens of 150×150×150mm. A series of 30 specimens were cast considering the effect of bar diameter, and concrete compressive strength. Test results showed that the load-slip behavior of the structural lightweight concretes (SLWCs) investigated compare reasonably well with the behavior of concretes reported in the literature, and is dependent upon the compressive strength, bar size and the embedded length. The bond strength of SLWCs increased with a higher concrete compression strength but decreased as the bar diameter was increased. Comparisons of measured bond strength with the ACI bond equations showed that for all cases the experimental bond strength values were higher than the design ones. However, the results indicate use of caution when applying bond formulas of normal weight concrete to lightweight concretes. Furthermore, this study has revealed that locally available natural lightweight aggregates could be considered as a promising, and cost effective material for designing reinforced concrete members.

Performances of Artificial Lightweight Geopolymer Aggregate (ALGA) in OPC Concrete

The non-availability of natural lightweight aggregate and demand are increasing in worldwide, thus new alternatives on producing artificial aggregate should be developed. This paper discussed on the mechanical properties of artificial lightweight geopolymer aggregate (ALGA) made from LUSI mud and alkaline activator in concrete. LUSI means Sidoarjo mud from Indonesia which erupted on 2006 with high volume and impacted an area of almost 770 hectare. The alkaline activator used was combination of sodium hydroxide and sodium silicate. The geopolymer paste formed need to be pelleted and sintered at 950 °C. The results showed that the compressive strength of OPC-ALGA concrete is 41.89 MPa at 28 days of testing with a density of 1760.1 kg/m3 which can be classified as lightweight concrete. The water absorption of ALGA concrete is 2.77%.

CONSTRUCTION POTENTIAL OF RECYCLED MASONRY FOR LIGHTWEIGHT CONCRETE

A sustainable and developing building industry requires large quantities of raw materials such as aggregates and crushed rocks. However, sourcing natural aggregates is becoming more problematic due to environmental impacts. Hence, the use of secondary materials, such as recycled aggregate can reduce the amount of natural aggregates required. Lightweight concrete is frequently used by the building industry, and it is commonly produced with natural lightweight aggregates such as scoria, which results in high production costs. Preliminary tests on recycled aggregates showed that recycled masonry has a similar specific gravity as scoria and relatively good strength. Hence, crushed masonry can be used to replace natural lightweight aggregates. This paper discusses the use of partial or total replacement of normal-weight aggregates with recycled lightweight aggregates, and its effects on the strength and elastic properties of concrete. It is shown that concrete mixes with recycled aggregates generate comparable results to mixes with scoria, but at lower production costs.

Reduction of the Early Autogenous Shrinkage of High Strength Concrete

The results of a laboratory investigation on the early autogenous shrinkage of high strength concrete, and the possibilities of its reduction, are presented. Such concrete demonstrates significant autogenous shrinkage, which should, however, be limited in the early stages of its development in order to prevent the occurrence of cracks and/or drop in the load-carrying capacity of concrete structures. The following possibilities for reducing autogenous shrinkage were investigated: the use of low-heat cement, a shrinkage-reducing admixture, steel fibres, premoistened polypropylene fibres, and presoaked lightweight aggregate. In the case of the use of presoaked natural lightweight aggregate, with a fraction from 2 to 4 mm, the early autogenous shrinkage of one-day-old high strength concrete decreased by about 90%, with no change to the concrete's compressive strength in comparison with that of the reference concrete.

Ductility of reinforced lightweight concrete beams and columns

This paper presents analytical and experimental results on ductility of reinforced lightweight concrete beams and columns in the form of moment curvature relationships, and compares the response with that of normal reinforced concrete members. The experimental part is limited to flexural tests on beams made of lightweight concrete. The latter is obtained with natural lightweight aggregates. Concrete and steel stress-strain models in compression and tension are integrated analytically through the section in order to derive the resulting moment and axial force. Lightweight concrete beams and columns showed a more ductile behavior than normal concrete members and the analytical model reproduced the response with very good accuracy. The lightweight ductility was more pronounced in columns subjected to axial compression forces and bending.