Properties Of Lightweight Aggregate Concrete Research Articles

Effect of Sand Content on the Workability and Mechanical Properties of Concrete Using Bottom Ash and Dredged Soil-based Artificial Lightweight Aggregates

The objective of this study is to examine the workability and various mechanical properties of concrete using artificial lightweight aggregates produced from expanded bottom ash and dredged soil. Fifteen concrete mixes were classified into three groups with regard to the designed compressive strengths corresponding to 18 MPa, 24 MPa, and 35 MPa. In each group, lightweight fine aggregates were replaced by using natural sand from 0 to 100% at an interval of 25%. Thus, the density of concrete ranged between 1455 and 1860 kg/m3. Based on the regression analysis using test data, a reliable model was proposed to clarify lower early-age strength and higher long-term strength gains of lightweight aggregate concrete (LWAC) when compared with the predictions of the fib model. The proposed model also indicates that a lower water-to-cement ratio is required with the decrease in the natural sand content to achieve the designed compressive strength of concrete. The partial use natural sand is favorable for enhancing the tensile resistance capacity, shear friction strength, and bond behavior with a reinforcing bar of LWAC. The fib model overestimates direct tensile strength, bond strength and the amount of slip at the peak bond stress of LWAC. Therefore, it is necessary to consider the density of concrete as a critical factor in conjunction with its compressive strength to rationally evaluate the various mechanical properties of LWAC.

Mechanical properties and microstructure of lightweight aggregate concrete with and without fibers

The effects of several factors such as dry apparent density, water-to-binder ratio, properties of expanded shale aggregates, and fiber volume fraction, on the mechanical properties of lightweight aggregate concrete (LWAC) were experimentally investigated. Performance of LWAC were characterized through compressive strength, splitting tensile strength and flexural strength. This paper characterizes the morphology and microstructure of lightweight aggregate and two types of interfacial transition zone (ITZ) by using scanning electron microscopy (SEM). More than 40 different LWAC mixtures included five different expanded shale aggregates and two types of fiber were designed and fabricated, exhibited 28-day compressive strength from 47 to 86 MPa for dry apparent density of 1720–1940 kg/m3, respectively. The test results shown that both water-to-binder ratio and lightweight aggregate properties have significant effects on the LWAC. Crushed shale aggregate with dense shell and low absorption was recommended. The addition of fiber had a slight impact on compressive strength but resulted in significant increases in splitting tensile strength and flexural strength. The maximum increase in strength was achieved at a volume fraction of carbon fibers of 0.9%. Furthermore, microstructure investigation revealed that a slight wall effect occurred in the ITZ of lightweight aggregate with a dense shell and low water absorption.

Comparative study of carbonized peach shell and carbonized apricot shell to improve the performance of lightweight concrete

To improve the performance of peach shell concrete (PSC) and apricot shell concrete (ASC), the effect of carbonized peach shell (CPS) and carbonized apricot shell (CAS) instead of peach shell (PS) and apricot shell (AS), respectively, on physical, mechanical and triaxial creep properties of lightweight aggregate concrete (LWAC) was investigated. Results showed that the replacement of raw aggregates (PS and AS) with carbonized aggregates (CPS and CAS) reduced the density, water absorption and open porosity, and increased the efficiency factor, total porosity of LWAC. Moreover, the mechanical properties were significantly enhanced, and the CAS mixture obtained the highest compressive strength, splitting tensile strength, flexural strength and modulus of elasticity, which were 38.8 MPa, 3.54 MPa, 5.49 MPa, and 15.1 GPa, respectively, an increase of 44.2%, 55.3%, 54.6%, and 42.5%, respectively, compared to the AS mixture. Triaxial creep results showed that under coupled water pressure and axial pressure condition, the use of carbonized aggregates instead of raw aggregates significantly decreased creep strain of LWAC and the concentrations of K+, Ca2+, Na+, Mg2+ and Sr2+ in the leaching solution. Therefore, use of CPS and CAS as lightweight aggregate in concrete can significantly improve the performance of LWAC.

Influence of Aggregate Gradation on the Engineering Properties of Lightweight Aggregate Concrete

Expanded shale lightweight aggregates, as the coarse aggregates, were used to produce lightweight aggregate concrete (LWAC) in this research. At the fixed water-cement ratio, paste quantity, and aggregate volume, the effects of various aggregate gradations on the engineering properties of LWAC were investigated. Comparisons to normal-weight concrete (NWC) made under the same conditions were carried out. From the experimental results, using normal weight aggregates that follow the specification requirements (standard gradation) obtained similar NWC compressive strength to that using uniform-sized aggregates. However, the compressive strength of LWAC made using small uniform-sized aggregates was superior to that made from standard-grade aggregates. This is especially conspicuous under the low water-cement ratio. Even though the workability was affected, this problem could be overcome with developed chemical additive technology. The durability properties of concrete were approximately equal. Therefore, it is suggested that the aggregate gradation requirement of LWAC should be distinct from that of NWC. In high strength LWAC proportioning, following the standard gradation suggested by American Society for Testing and Materials (ASTM) is optional.

Strength degeneracy of LWAC and flexural behavior of LWAC members after fire

The characteristics of lightweight aggregate (LWA) with a low specific gravity and high water absorption will significantly change the properties of lightweight aggregate concrete (LWAC). This study aimed at exploring the effect of presoaking degree of LWA on the strength degeneracy of LWAC and flexural behavior of LWAC members exposed to elevated temperatures. The residual mechanical properties of the LWAC subjected to elevated temperatures were first conducted. Then, the residual load tests of LWAC members (beams and slabs) after exposure to elevated temperatures were carried out. The test results showed that with increasing temperature, the decreasing trend of elastic modulus for LWAC was considerably more serious than the compressive strength. Besides, the presoaking degree of LWA had a significant influence on the residual compressive strength and elastic modulus for LWAC after exposure to 800C. Moreover, owing to different types of heating, the residual load bearing capacity of the slab specimens were significantly different from those of the beam specimens.

Experimental study on the thermal properties of lightweight aggregate concretes at different moisture contents and ambient temperatures

This study reports the influence of moisture content and temperature on the thermal properties of lightweight aggregate concretes. Seven types of coarse and fine lightweight aggregates from three different natures were used. The thermal tests were performed on concrete samples at three different moisture conditions: dry state, partial saturation state and saturated state. At the dry state, measures have been taken at four different temperatures: 5°C, 20°C, 35°C and 50°C. The results show a great dependence of thermal conductivity and specific heat of lightweight aggregate concretes on the moisture content. However, concrete thermal diffusivity is not much influenced by the moisture state. These variations are discussed as a function of the type of lightweight aggregate and it volume fraction. The thermal conductivity increases with the temperature between 5 and 35°C and then stabilizes between 35 and 50°C.

Engineering properties of lightweight aggregate concrete containing binary and ternary blended cement

Lightweight concrete (LAWC) has numerous advantages over normal weight concrete (NWC), such as less dead load and construction costs. Using lightweight aggregates (LWA) is one of the most typical methods of fabricating structural LWAC. This paper studies the possibility of LAWC production by agricultural solid waste, specifically oil palm shell (OPS) and also by replacing ordinary Portland cement (OPC) with rice husk ash (RHA) and fly ash (FA) up to 50%. The effect of cement replacement with 0%, 10%, 20% and 30% of RHA (binary blended cement) and with 15%FA/15%RHA and 25%FA/25%RHA (ternary blended cement) on several engineering properties (workability, density, compressive strength, flexural strength, water absorption, drying shrinkage and ultrasonic pulse velocity) of OPS concrete was analyzed. The impact of 2, 4, and 6 days of water curing on 28-day compressive strength was examined as well. This study proved the possibility of fabricating sustainable LAWC made of high volume agricultural and industrial waste materials. Although the high amount of RHA in OPS Concrete caused reduction of compressive strength and workability, incorporating FA along with RHA addressed this issue. OPS concrete showed to be more sensitive to curing and only 4-day initial curing decreased the strength reduction up to 26% compare to air dry curing. Grades 30 (with OPC content of 350 kg/m3) and 25 (with OPC content of 250 kg/m3) green LAWC were successfully produced by incorporating 30% and 50% of RHA/FA respectively. In addition, significant CO2 reduction, as high as 41%, is calculated in this work to be emitted for manufacturing studied sustainable concretes.

Effect of presoaking degree of lightweight aggregate on the properties of lightweight aggregate concrete

This study aimed at exploring the effect of presoaking degree of lightweight aggregate (LWA) on the fresh and hardened properties of concrete. Two series (i.e., Series A and Series B) of concrete mixes that were made of LWA with different moisture states were prepared. The presoaking degree of LWA was divided into three types: oven dry state, 1 hour prewetted and 24 hours prewetted. For the Series A, the water content of the lightweight aggregate concrete (LWAC) mixes was adjusted in accordance with the moisture condition of the LWA. Whereas the amount of water added in the Series B mixes was deliberately not adjusted for the moisture condition of the LWA. Slump test, mechanical tests, interfacial transition zone microscopical tests and thermal conductivity test were carried out on the specimens of different concretes and compared with control normal-weight aggregate concretes. The test results showed that the effect of mixing water absorption by LWA with different moisture states was reflected in the fresh concrete as the loss of mixture workability, while in the hardened concrete as the increase of its strength. With the use of oven-dried LWA, the effect of reduction of water-cement ratio was more significant, and thus the microstructure of the ITZ was more compact.

Engineering properties of lightweight aggregate concrete containing limestone powder and high volume fly ash

Concrete industry is one of the major sources of consuming high volume of natural resources. On the other hand, cement industry is a significant point source of carbon dioxide emissions due to the decomposition of raw material and burning fuel during the manufacturing process. As the demand for concrete is growing, one of the effective way to minimize the negative environmental impact of the industry is the use of waste and by-product materials as cement and aggregate replacement in concrete.In the current study, possibility of making structural lightweight aggregate concrete using large amounts of waste material was investigated. The waste materials comprised oil palm shell, which was used as coarse aggregate, and a high volume (50% and 70%) of type F fly ash, as cement replacement by mass. The mechanical properties, such as compressive strength in different curing conditions, splitting tensile and flexural strengths, as well as density, ultrasonic pulse velocity, water absorption, and drying shrinkage up to one year were investigated. All oil palm shell concretes containing high volume fly ash are found to have adequate strength for formwork removal. Oil palm shell concretes containing high volume fly ash had 46%–60% lower cement content compared to previous studies with a similar compressive strength. Although, using high volume fly ash in oil palm shell concrete significantly reduced short-term mechanical properties, however, the use of limestone powder significantly improved the compressive strength at early and later ages. Test results also showed that there is no significant difference between the drying shrinkage of oil palm shell concrete containing 50% fly ash and the control oil palm shell concrete.

Investigation on mechanical properties and microstructure of high performance polypropylene fiber reinforced lightweight aggregate concrete

The purpose of this study is to investigate the effect of high performance polypropylene (HPP) fiber on the mechanical properties of lightweight aggregate concrete (LWC). The mechanical properties include the compressive strength, splitting tensile strength, flexural strength, flexural toughness and the impact resistance. Two types of interfacial transition zone (ITZ) at aggregates/cement paste and fibers/cement paste were investigated by using Scanning Electron Microscope (SEM). The experimental results showed that the addition of HPP fibers in LWC could significantly improve its mechanical properties. The flexural strength, splitting tensile strength, flexural toughness and impact resistance were enhanced while no obvious effect on compressive strength could be found. Adding proper amount of HPP fibers to LWC significantly improves its post-cracking behavior. Due to better bond property between aggregates and cement paste than that between fibers and cement paste, the aggregate-paste interface is not the weakest link in LWC. When the addition of HPP fibers is increased beyond 9kg/m3 (0.95% Vol.), the dispersion of fibers becomes very difficult. Based on various mechanical strengths, to enhance the mechanical properties of concrete, the optimal fiber content of 9kg/m3 (0.95% Vol.) is recommended.

Valorisation of waste expanded polystyrene in concrete using a novel recycling technique

This study examines the engineering properties of lightweight aggregate concretes (LWACs) incorporating a novel Expanded Polystyrene (EPS)-based lightweight aggregated called Stabilised Polystyrene (SPS). The SPS aggregate was produced by 80% waste EPS, 10% clay and 10% cement. The influence of the increasing incorporation of SPS on the workability, density, compressive strength, flexural strength, ultrasonic pulse velocity, drying shrinkage, expansion and water absorption (WA) of the different concretes has been investigated. The results showed that the use of SPS enabled to reduce the density of concrete by 8–52% compared to that of the control concrete. The reduction in density was due to the increase in total porosity in the lightweight concretes (LWCs), which also induced higher WA, drying shrinkage and expansion. The 28-day compressive strength of the LWAC was in the range of 4.6–16.4 MPa; thus, the concrete mixture with the higher performances almost satisfied the mechanical and density criteria of structural LWC. These results show that the utilisation of SPS for the manufacture of LWACs is possible.

Mechanical and thermophysical properties of lightweight aggregate concretes

In this study, experimental investigation is performed for producing new cement-based with relatively high strength, low density and good thermal properties for energy efficient buildings. Different types of concretes containing silica fume (SF), superplasticizer (SP) and air-entrained admixtures are prepared with a constant water–cement ratio, and normal aggregates replaced by lightweight aggregates (LWAs) including pumice (PA), expanded perlite (EPA) and rubber aggregates (RA) at different volume fractions of 10%, 20%, 30%, 40% and 50%. 102 samples with different materials and compositions are produced, and their characteristics are tested in accordance with ASTM and EN standards. Based on the experimental results, equations are presented to determine the relation between the thermophysical properties of composite samples. The investigation revealed that the addition of PA, EPA and RA reduced the material bulk density and compressive strength, and improved the insulation characteristics of the composite concretes. Furthermore, it was found out that the reductions in thermal conductivity and diffusivity of the produced samples reached to 82% and 74%, respectively.

Effects of rubber particles on mechanical properties of lightweight aggregate concrete

This paper presents the compiled experimental data of slump value, compressive strength, splitting tension strength, flexural strength, static modulus of elasticity and unit weight for eleven different mixtures of rubber lightweight aggregate concretes cured up to 1, 7 and 28days. The eleven different mixtures cover one fundamental mixture and ten different replacements of rubber particles for sand volume from 10% to 100%. Based on the experimental results, incorporating rubber particles profoundly has a detrimental effect on the slump and mechanical strength, while the unit weight of concrete dropped. The static modulus of elasticity decreased from 24.1GPa to 6.3GPa with the replacement of rubber particles increasing from 0% to 100%. The toughness of rubber lightweight aggregate concretes is obvious superior to the plain lightweight aggregate concretes. The application of rubber particles in lightweight aggregate concretes provides further opportunity to recycle waste tires.

Use of Furnace Bottom Ash for producing lightweight aggregate concrete with thermal insulation properties

The influence brought by Furnace Bottom Ash (FBA) incorporation on the properties of lightweight aggregate concrete was studied systematically. In total, six mixtures of concrete targeted at a 28 d compressive strength of 30 MPa were designed, including one control mix made with all normal weight aggregates and at a water/cement ratio (w/c) of 0.6, and another five lightweight aggregate concrete mixes at a w/c of 0.39 by using 0, 25%, 50%, 75% and 100% FBA replacing natural fine aggregate (crushed fine stone). The testing results of the hardened concrete properties showed that, for the lightweight aggregate concrete using 100% FBA to replace crushed fine stone, a 28 d oven-dried density of about 1500 kg/m3 was obtained. The test results showed the lightweight aggregate concrete had lower strength and stiffness compared to the normal aggregate concrete. But in terms of the effectiveness of strength provided by unit weight of concrete indicated by compressive strength in MPa divided by saturated-surface dried (SSD) density in g/cm3, fc/D, a satisfactory ratio can be obtained when not more than 50% FBA was used to replace the crushed fine stone. The durability property indicated by the chloride ion penetration test shows the lightweight aggregate concrete with FBA had high chloride ion penetrability. The heat insulation property (thermal conductivity K-value) test demonstrated that by using the porous lightweight aggregate, the thermal conductivity could be lowered to around 70% of the control. When more FBA was used to replace crushed fine stone, the thermal conductivity value could be further reduced. The results of this study demonstrated it is feasible to produce lightweight aggregate concrete with high volume of FBA incorporation for building insulation uses.

Surface Properties of Lightweight Aggregate Concrete and its Correlation with Durability

Durability is one of most important requirements of concrete design. From this aspect is arising the required minimal compressive strength class of conventional concrete in order to ensure durability. The porosity of cement mortar matrix and consequently the liquid and gas permeability of concrete may be reduced. But the strength of lightweight aggregate concrete depends primarily on the crushing resistance of lightweight aggregate (LWA). With low strength LWA may be achieved higher concrete strength by high strength cement mortar matrix. Therefore we can not consider durability simply on the basis of the compressive strength of concrete. The most important durability factors are closely related to the porosity and strength of the cement mortar matrix but for example the abrasion resistance depends more significantly on the aggregate type. Lightweight aggregates usually do not have high abrasion resistance, but they can be advantageous in case of restoration of bridge pavement. The most important factors of durability regarding pavements are frost scaling and abrasion resistance. These parameters (especially abrasion resistance) are not available in the literature when using LWA.

Effects of particle characteristics of lightweight aggregate on mechanical properties of lightweight aggregate concrete

Particle characteristics of lightweight aggregates (LWAs) have great influences on the mechanical performance of the corresponding concrete. In this research, particle characteristics of LWAs were measured through digital image processing (DIP), including particle sizes, gradation and shape properties, and the effects of LWA particle characteristics on mechanical performances of lightweight aggregate concrete (LWAC) were investigated through grey correlation analysis methods. The LWAC interfacial roughness was investigated with fractal theory, and the effects of LWA particle characteristics on the LWAC interfacial roughness were also investigated through grey correlation analysis methods. The results show that LWAC interfacial fractal dimension and mechanical performance exhibit good linear correlation. LWA particle specific surface area and LWA particle aspect ratio take greater effects on LWAC mechanical strength and interfacial roughness. LWAC mechanical strength would be greater when LWA specific surface area (SV) was within 586.4–633.7m2/m3 and LWA aspect ratio was within 1.3262–1.3308. LWAC interfacial fractal dimension (D) would be greater when LWA specific surface area (SV) was within 539.1–633.7m2/m3 and LWA aspect ratio was within 1.3262–1.3354. It is proposed that the change of the contact area between LWA particles and mortar phases will change the occlusal structures on the LWAC interface, which consequently changes the interfacial roughness, the interfacial bond strength and hence the LWAC mechanical strength.

Studying the effect of various parameters on mechanical properties of lightweight aggregate concrete using MANOVA

In order to reduce the dead load of the structures prone to seismic hazards and improve the insulating characteristics of construction materials with the purpose of economical construction, lightweight aggregate (LWA) concrete (LWAC) could be pondered. In this paper, the effect of different parameters such as volume fraction, LWA grading and sand to cement ratio on compressive strength, and elastic modulus of lightweight concrete have been studied. In this study, 36 different mix designs were developed; 3 different sand to cement ratios, 4 volume fractions and 3 different gradings of LWA were considered in order to study the effect of these parameters and find out an efficient mix design for structural use. In order to investigate the effect of each parameter on the compressive strength and elastic modulus, a multivariate analysis of variation was performed. Results indicate that the volume fraction and the LWA grading are the two key parameters influencing compressive strength comparing with sand to cement ratios. Moreover, it was concluded that the sand to cement (S/C) ratio could be as effective as other parameters on elastic modulus of LWAC.

Mechanical and thermal properties of lightweight concretes with vermiculite and EPS using air-entraining agent

This study aimed to compare mechanical and thermal properties of lightweight aggregate concrete with two kinds of lightweight aggregates, vermiculite and Expanded Polystyrene (EPS) and using air-entraining agent and superplasticizer admixture. For better reliability, a statistical analysis of the results compressive strength and density was used. The factors of the 22 full factorial design were: amount of lightweight aggregate (55% and 65%) and quantity of air-entraining agent (0.5% and 1.0%). The results showed that the addition of air-entraining agent left the lightweight concretes even lighter, but less resistant. EPS lightweight concrete has higher strength and is lighter than with vermiculite. Vermiculite lightweight concrete had lower thermal conductivity than with EPS. The better lightweight aggregate content was 55%.

Enhancement of shrinkage behavior of lightweight aggregate concretes by shrinkage reducing admixture and fiber reinforcement

This paper presents the results obtained from an experimental study conducted to investigate the effect of shrinkage reducing admixture (SRA) and steel fiber addition on the performance properties of lightweight aggregate concrete (LWAC). Total of seven LWAC mixes with SRA or steel fibers were produced at the same water-cement ratio using cold-bonded fly ash coarse aggregates. The percentage of steel fiber volume fractions used in the mixes was 0.25, 0.75 and 1.25. The amount of SRA used in the mixes was 0.75%, 1.5% and 3 % by weight of cement. Ring type specimens were used for the restrained shrinkage cracking test. At the same time, free shrinkage and weight loss of LWACs were measured. Moreover, the compressive and split tensile strength tests were undertaken. The results indicated that the use of steel fibers has little effect on compressive strength but it improves the split tensile strength. The addition of SRA decreases compressive strength without affecting tensile strength. Moreover, the utilization of steel fiber or SRA extends the cracking time and reduces the crack width of LWAC resulting in finer cracks associated with lower free shrinkage.

Influence of the volume fraction and the nature of fine lightweight aggregates on the thermal and mechanical properties of structural concrete

The results of investigations on thermal and mechanical properties of lightweight aggregate concretes according to mixture parameter are reported. Seven types of fine and coarse lightweight aggregates from three different natures were used. The aggregates in mixes were a combination of coarse lightweight aggregate with fine normal-weight aggregate and/or fine lightweight aggregate. The replacement of fine normal weight aggregate by fine lightweight aggregate reduces concrete strength but improves its thermal performance. Detailed analysis of the influence of the nature and quality of aggregates on the concrete properties is provided. The experiment data allows to investigate the relation between mechanical properties and thermal conductivity for studied concretes in order to optimize the strength/insulation ratio. A wide range of “insulated” lightweight aggregate concretes is performed whose strength class ranges from LC20/22 to LC40/44 and thermal conductivity ranges from 0.43 to 0.73W/mK.