Lightweight Aggregate Content Research Articles

Applied development of sustainable-durable high-performance lightweight concrete: Toward low carbon footprint, durability, and energy saving

Over the past few decades, the utilization of Lightweight Concrete (LWC) has emerged as a promising solution for reducing the dead load of structures. However, a key concern associated with the reduction of concrete density, is the potential decrease in mechanical and durability properties. This paradox necessitates a precise mix design that fulfills the requirements of high-strength concrete. This article investigates the influence of Lightweight Expanded Clay Aggregate (LECA) on the strength and durability, and thermal conductivity of Lightweight High-Performance Concrete (LWHPC). The LWHPC mixes explored in this study include sustainable cement solutions such as Portland limestone cement, varying water/binder ratios of 0.3 and 0.35, Leca contents ranging from 5 % to 20 % by volume, and two different pozzolanic supplements, namely silica fume and fly ash, which can be reducing porosity and enhancing durability and mechanical strength. The durability properties of the concrete were assessed through water absorption, electrical resistivity, and chloride migration profiles. Additionally, thermal conductivity measurements were conducted on all specimens. The results indicate that LWHPC, with a lower water/binder ratio, exhibits higher compressive strength and lower absorption, indicating good concrete quality. Generally, after a curing period of 90 days, mixtures with a density exceeding 1700 kg/m3 demonstrated superior durability characteristics. Furthermore, LWHPC mixes in both water/binder ratio groups displayed significantly low thermal conductivity with increasing lightweight aggregate content.

An investigation of the hybrid effect of pre-absorbed lightweight aggregate and basalt-polypropylene fiber on concrete performance

Although fibers have been extensively adopted to modify the mechanical performance of concrete containing lightweight aggregate (LWA), the composite impact of fibers and LWA’s internal curing has not been addressed yet. In this study, a comprehensive investigation of basalt-polypropylene (BF-PF) fiber reinforced lightweight aggregate concrete was carried out to investigate the interactions between BF-PF fibers and LWA’s internal curing, considering multiple LWA contents and BF:PF ratios. Results showed that adding LWA benefited the flexural strength but lowered the compressive strength, as the multi-pore structure of LWA increased the porosity and pore size of concrete while the internal curing of LWA optimized the overall pore structure. Nonetheless, adding BF-PF fibers could alleviate LWA’s negative effect on compressive strength given that a positive hybrid effect was identified between LWA and BF-PF fibers. The discharged water from LWA benefited cement hydration and contributed to an increased Ca(OH)2 content in the paste and a lowered Ca/Si ratio in the interfacial transition zone, thereby enhancing the bond between BF-PF fibers and the paste. Given a fixed fiber volume, increasing the PF ratio was more conducive to concrete’s post-cracking behavior while increasing the BF ratio benefited concrete’s pore structure. Furthermore, a multi-dimensional evaluation accommodating fresh properties, mechanical performance, pore characteristics, cost and environmental sustainability indicated that a mix of 20% LWA and 0.20% fiber at a BF:PF ratio of 3:1 was the optimum one. The results demonstrate the enhancing mechanism of fiber reinforced lightweight aggregate concrete, providing insight into concrete design in practical engineering.

3D printing lightweight aggregate concrete prepared with shell-packing-aggregate method - Printability, mechanical properties and pore structure

It is a challenge to use porous lightweight aggregates to prepare 3D printing concrete as the water absorption process of porous lightweight aggregates has significant effect on its printability, especially when the content of lightweight aggregate is relatively high. In this paper, the effects of preparation methods on the rheological properties and printability of 3D printing lightweight aggregate (3DPLWC) are studied, aiming to prepare 3DPLWC with high lightweight aggregate content. 3DPLWC with 50, 75 and 100 vol.-% substitution of fine river sand with clay ceramsite sand (CCS) are successfully prepared with shell-packing-aggregate method. The mechanical properties and pore structure of 3DPLWC with different CCS contents are then studied. It is found that the printing process has caused the anisotropy of 3DPLWC, and the specific strength of 3DPLWC is lower than cast counterparts. For 3DPLWC, the increase of pre-wetted CCS content contributes to the decrease of matrix porosity and the increase of circularities of matrix pores in the printed specimens. The results of this study can provide guidance for the preparation of 3DPLWC with different density levels.

Mechanical and Microstructural Properties of Ultra-High Performance Concrete with Lightweight Aggregates

Although ultra-high-performance concrete (UHPC) presents superior mechanical properties and durability compared to conventional concrete; its spalling resistance to elevated temperatures is much lower compared to conventional concrete due to the high compactness and absence of capillary pores. This paper investigated the influence of lightweight aggregate (LWA) on the strength properties and microstructure of UHPC to enhance its resistance to elevated temperatures. UHPC specimens prepared with LWA as a partial replacement of silica sand were produced. The study evaluated the compressive and flexural strengths, failure mode, mass loss, and microstructure of the specimens, using SEM. The results showed that the compressive strength of the UHPC specimen was reduced with increasing the content of LWA at ambient temperature, but the compressive strength of the UHPC specimens prepared with LWA improved when exposed to elevated temperatures. The replacement of 10% of the silica sand with LWA led to an increase in the compressive strength from 100 MPa to 110 MPa after exposure to 200 °C; however, the flexural strength decreased from 23.6 MPa to 18.3 MPa. On the contrary, the flexural strength of UHPC increased with the inclusion of LWA at an ambient temperature but reduced with high-temperature exposure. The failure mode of UHPC was not significantly affected by the variation in LWA content and temperature. In addition, the SEM result confirms that LWA is an effective internal curing material for enhancing the microstructure and compressive strength of UHPC

Tensile creep behavior of Alkali-activated slag concrete incorporating lightweight aggregate

This study aims to investigate the effect of pre-wetting lightweight aggregate (LWA) on the tensile creep of alkali-activated slag concrete (AASC) for 14 d. Three replacement rates of natural coarse aggregate with LWA were used in this study, including 0, 50%, and 100%, and the Ordinary Portland cement concretes (OPCCs) mixed with LWAs were considered as control samples. The results showed that the tensile creep of the AASCs was higher than those of OPCCs with the same LWA content. The incorporation of pre-wetting LWA significantly reduced the modified autogenous shrinkage and tensile creep of the AASCs, and the magnitudes were continuously declined with the increase in LWA contents. The early age of 1 d dominated more than 70% of the total tensile creep of the AASCs for 14 d. Furthermore, pre-wetting LWAs had a greater effect on decreasing tensile creep for the AASC system than the OPCC system. Meanwhile, the creep/shrinkage ratio of the AASCs was declined by the addition of pre-wetting LWAs. In addition, the cracking age of the AASC was desirably delayed by adding pre-wetting LWA, and the effect was more noticeable with the increase in LWA contents.

Mechanical properties of alkali-activated slag lightweight aggregate concrete

The mechanical properties of alkali-activated slag lightweight aggregate concrete (AAS-LWAC) were deep investigated. A total of 108 AAS-LWAC samples were prepared for compressive strength test, splitting tensile strength test, and flexural strength test. The microstructures of AAS-LWAC were characterised in depth using scanning electron microscopy (SEM). Compared with clay ceramsite and shale ceramsite as the lightweight aggregate (LWA), AAS-LWAC with fly ash ceramsite as the LWA exhibited the highest compressive strength. Besides, the compressive, splitting, and flexural strengths of AAS-LWAC decreased with increasing LWA content. Moreover, compared with polypropylene fibres and basalt fibres, steel fibres can significantly increase the compressive, splitting, and flexural strengths of AAS-LWAC, with an optimal volume content of 0.6% steel fibre. Furthermore, a modified formula for the variation in compressive strength of AAS-LWAC over time was proposed, considering the influence of LWA.

Residual mechanical properties of concrete containing lightweight expanded clay aggregate (LECA) after exposure to elevated temperatures

AbstractThe mechanical properties of light‐weight concrete (LWC) in fire are known to be better than those of normal‐strength concrete (NSC), both at high temperature (hot properties) and after cooling (residual properties). The objective of this paper is to increase the knowledge of LWC's residual properties by testing a number of mixes containing expanded clay as light‐weight coarse aggregate. An experimental program was carried out, in which one normal‐weight concrete mix and two lightweight aggregate mixes containing different amounts of LECA were used to fabricate 72 concrete cylinders and 36 concrete prisms. All mixes contained silica fume as a supplementary cementitious material. The specimens were tested at the ambient temperature and after exposure to temperatures of 250, 500, and 750°C to obtain their compressive and tensile strength, modulus of elasticity, and stress–strain response. Results indicate that exposure to temperatures up to 250°C has no significant effect on the mechanical properties of concrete containing LECA just as in normal weight concrete. However, with increasing the temperature, increasing the lightweight aggregate content of the mix resulted in better strength retention after exposure to elevated temperatures. The experimental data are also used to develop equations to evaluate the residual mechanical properties of concrete.

Combined effects of microsilica, steel fibre and artificial lightweight aggregate on the shrinkage and mechanical performance of high strength cementitious composite

In this study, the effects of micro-steel fiber, pelletized fly ash lightweight aggregate and microsilica content on the fresh and hardened properties of high-performance cementitious composite (HPCC) were experimentally investigated. Micro-steel fibers having a length of 6 mm were used in the production of mixtures at the level of 0%, 1% and 2% by total volume. Besides, artificial lightweight aggregate produced by the pelletizing method was employed in the mixture production by 0% and 20% of total aggregate volume. 0% and 25% of the total binder content were designated as microsilica. Thus, a total of 12 different HPCC mixtures were obtained. The water-to-binder ratio of 0.2 was chosen in the design of all HPCC mixtures. A high-rate water-reducing chemical admixture is used to give a suitable flow for the fresh mixtures. The mechanical properties of HPCC mixtures are evaluated in terms of compressive and flexural strengths and elastic modulus. In addition to these, total water absorption and capillary water absorption tests were performed to evaluate the pore structure and permeability. The drying and autogenous shrinkage values were determined during the 60-day drying period. Thus, the effects of fiber content, microsilica addition, and artificial lightweight aggregate content were examined. The results of the experiment showed that the mechanical properties of HPCC and shrinkage behavior have been improved with the increase of steel fiber volume fraction. Furthermore, the negative effects of artificial lightweight aggregate can be eliminated by microsilica.

Lightweight aggregate concrete produced with crushed stone sand as fine aggregate

Lightweight aggregate concrete mixtures incorporating 0, 10, 20, and 30 weight percent replacement of normal-weight aggregate with lightweight aggregate and crushed stone as fine aggregate were tested at 7, 28, 56, and 90 days for various strength and durability characteristics of hardened concrete. Test results indicated that compressive, flexural, and split tensile strengths and static modulus of elasticity of concrete mixtures reduced with an increase in the percent replacement of normal-weight aggregate with lightweight aggregate. Furthermore, the volume of permeable voids and hence moisture sorption in lightweight aggregate concrete reduced as the lightweight aggregate content was increased pointing at the enhanced durability of the lightweight aggregate concrete mixtures. A significant reduction in dry density of hardened concrete was recorded due to the inclusion of lightweight aggregate in concrete mixtures. Considering the strength and reduction in dry mass, 20 wt.% replacement of normal-weight aggregate with lightweight aggregate is considered to be an optimum level. Reduced density of lightweight aggregate concrete mixtures is viewed as a major source of economical design of structural members as the lower concrete density will result into a reduction of self-weight of the structural members, which will allow the economical structural design of such members with smaller cross-sections. Test results of this work also showed the viability of 100% replacement of desert sand with crushed stone sand as fine aggregate towards the production of lightweight aggregate concrete.

Dynamic modulus of elasticity of geopolymer lightweight aggregate concrete

The production processes of ordinary Portland cement (OPC), accompanying with bad environment influences such as, huge energy consumption, greenhouse gases emissions and natural resource exploitation; but fly ash-based geopolymer concrete is produced without (OPC), yet that has many sustainable environment benefits. In this study locally artificial lightweight aggregate was used to produce lightweight fly ash geopolymer concrete. The dynamic modulus of elasticity for geopolymer lightweight concrete produced by using locally artificial aggregate was investigated. Reference lightweight geopolymer concrete containing natural normal weight fine aggregate without fiber, lightweight geopolymer concrete reinforced with two volume fractions of steel fibers (0.25 and 0.5); in addition to four concrete mixtures containing artificial coarse lightweight aggregate and artificial lightweight fine aggregate with 25, 50, 75 and 100% volumetric replacement to natural normal weight fine aggregate (sand) were prepared. The dynamic modulus of elasticity was tested at 28day age for all specimens using resonance frequency method. The results demonstrate that the incorporation of artificial fine lightweight aggregate as a volumetric replacement to natural fine aggregate in concrete geopolymer lightweight concrete reduces the dynamic modulus of elasticity gradually with the increase of artificial lightweight aggregate content.

Bond to reinforcement of polymeric lightweight flowable concrete for structural applications

Limited studies investigated the effect of styrene-butadiene rubber (SBR) latexes on bond properties of structural lightweight self-consolidating concrete (LWSCC). The mixtures tested in this investigation were prepared using expanded kaolinic clay lightweight aggregate (LWA), while the water-to-binder ratio was adjusted to secure compressive strength of 40 ± 3.5 MPa. Testing was realized using the beam-end specimen method, and the parameters under evaluation included the LWA content (up to 40% of coarse aggregate volume), SBR dosage (up to 15% of binder mass), and bar diameter. Test results have shown that the initial stiffness of load vs. slip curves and ultimate bond strength of LWSCC considerably improved with SBR inclusion. This was related to the coupled effect of the SBR polymers that help relaxing stresses during loading and presence of LWA that reduces bleeding and promotes creation of hydration compounds at the steel-concrete transition zone. The experimental data are compared with the design bond strengths determined by CEB-FIP Model Code 2010, ACI 318-14, and European Code EC-2.

The influence of lightweight aggregate, freezing–thawing procedure and air entraining agent on freezing–thawing damage

This article presents the results of a study dealing with the concrete resistance to repeated cycles of freezing and thawing of nonair entrained, fine lightweight aggregate (LWA) and air‐entrained concrete when tested in accordance with ASTM C 666, procedures A and B. The water‐to‐binder ratios (w/b) of the mixtures ranged from 0.25 to 0.35, and the percentage of cement replacement by silica fume were 7% on a weight basis and constant throughout study. Binder dosage was 500 kg/m3 and constant. LWA was pumice aggregate (PA) and expanded perlite aggregate (EPA). PA and EPA were replaced by 10, 20, and 30% of total volume of 1 m3 as a fine aggregate (0–2 mm fine aggregate fraction). Also one group was produced with air entraining agent by 0.1% ratio of binder dosage. The 200 freeze–thaw cycles were carried out according to ASTM C666/C666M‐15, procedure A and B. The compressive strength, ultrasonic pulse velocity, relative dynamic modulus of elasticity and dry unit weight of mixtures were investigated. Based upon the analysis of the test data, it is concluded that samples contain air‐entrained agent and 10% LWA were more durable than that of control sample. With the increasing of the LWA content the freeze–thaw resistance of samples decreased. Thus, higher content of LWA is not recommended when it is to be subjected to repeated freeze–thaw cycles. Freezing–thawing procedures were compared with each other and found that procedure A was more severe than procedure B.

Combined Effects of Densified Polystyrene and Unprocessed Fly Ash on Concrete Engineering Properties

The present study evaluated the combined effects of two types of waste materials of expanded polystyrene (EPS) and unprocessed fly ash (FA) on different properties of concrete. A novel recycling technique of densifying waste EPS is used to produce a novel lightweight aggregate (LWA). This new technique has solved the problem of segregation in concrete by coating EPS particles with a natural binder of clay and cement. Nine different concrete mixtures with a water to cement ratio of 0.8 were used. The densified EPS and unprocessed FA were partially replaced with natural aggregate and Portland cement, respectively. The engineering properties, including workability, density, compressive strength, ultrasonic pulse velocity (UPV), and water absorption (WA) were investigated at different curing times. According to the experimental results, there is a decrease in compressive strength and UPV with increasing this novel LWA content in concrete. However, by using a suitable mix design, the utilisation of these two waste materials in concrete using an appropriate recycling technique is possible.

Feasibility of assessing segregation in internally cured mortar based on the variation of properties

This paper focuses on the feasibility of assessing the segregation of internally cured mortar accompanying lightweight aggregate (LWA) by quantifying the variation of pore-related properties between top and bottom layers of mortar. Twelve internally cured mortars, with different LWA contents, were prepared. Dry and saturated densities, dynamic modulus and water absorption of hardened mortar at 1day, 7 and 28days were tested. Sensitivity of the properties to LWA content was analyzed by linear regression. Experiment errors of tests were compared. Multiple comparisons, a method of Analysis of Variance (ANVOA), was adopted to reveal the significance of variations. The results show that, densities and dynamic modulus varied linearly with the LWA content but not for water absorption. The experiment errors of densities tests are far lower than that of dynamic modulus and water absorption tests. It is revealed that saturated density is the most suitable property to evaluate the segregation of internally cured mortar.

Influence of the artificial lightweight aggregate on fresh properties and compressive strength of the self-compacting mortars

The current study experimentally investigated the effect of the artificial lightweight aggregate and the water-to-binder ratio on the initial and final setting times of self-compacting mortars. The artificial lightweight aggregates used in this study were manufactured through cold bonding pelletization of 90% of class-F fly ash and 10% of Portland cement in a tilted pan with an ambient temperature and moisture content. The self-compacting mortars were designed at four binder contents of 540kg/m3, 520kg/m3, 500kg/m3, and 480kg/m3 at four different water-to-binder ratios of 0.33, 0.37, 0.40, and 0.44, respectively. In each water-to-binder ratio, the natural aggregate was substituted with the artificial lightweight aggregate at the replacement levels of 0%, 20%, 40%, and 60%. Totally 16 self-compacting mortar mixtures were designed and produced. Slump flow diameter, V-funnel flow time and initial and final setting times were experimentally investigated as fresh properties while the compressive strength of the mortar mixtures were measured at 5 different ages of 3-day, 7-day, 28-day, 56-day, and 90-day. Test results showed that both initial and final setting times of the self-compacting mortars were significantly affected by the water-to-binder ratio. Addition to setting times, the slump flow diameter and V-funnel flow time was influenced by both the water-to-binder ratio and the artificial lightweight aggregate content. Moreover, the compressive strength results indicated that increasing the artificial lightweight aggregate content systematically decreased the compressive strength of the mortar mixtures at aforementioned testing ages whereas decreasing the water-to-binder ratio increased the compressive strength.

Investigation on Fracture Performance of Lightweight Epoxy Asphalt Concrete Based on Microstructure Characteristics

AbstractIn order to investigate the fracture performance of lightweight epoxy asphalt concrete (LEAC) used in steel bridge deck pavement, experiments and numerical simulations were used to analyze the effect of lightweight aggregate (LWA) on fracture behavior of LEAC. The gradations of LEAC with different LWA contents were determined by the Marshall method, indirect tensile test with and without freeze-thaw processing were used to measure the indirect tensile strength and moisture stability of LEAC, and fracture properties were evaluated by three-point bending beam test at 15°C and −10°C. Also, internal structures of LEAC were scanned by X-ray CT device to develop three-dimensional finite element models (3D-FEM), and mechanical states of basalt aggregate, LWA, and epoxy asphalt mastic (EAM) were also studied. The results show that the LWA has an obvious influence on fracture properties of LEAC; LWA content 5% can significantly improve the fracture performance. EAM is the main bearing structure of LEAC; mi...

Experimental evaluation of cement mortars with phase change material incorporated via lightweight expanded clay aggregate

ObjectiveAn experimental evaluation on cement mortars with phase change material (PCM) incorporated via lightweight aggregate (LWA) is reported. Materials and methodsThree groups of LWA mortars were produced: one with pre-soaked LWA and the others with PCM-filled LWA combining two different impregnation processes and PCM dosages of 50, 75 and 100kg/m3 corresponding to the LWA contents of 242, 354 and 481kg/m3, respectively. Mechanical and thermophysical properties were evaluated. ResultsThe results showed that high thermal inertia and low mass are compatible in PCM-filled LWA mortars and that the thermal response increases with the PCM to a certain limit and then decrease.

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%.

Effect of steel fiber addition and aspect ratio on bond strength of cold-bonded fly ash lightweight aggregate concretes

In this study, the adherence between reinforcing steel bar and the cold bonded fly ash lightweight aggregate concretes (LWAC) with and without steel fiber were evaluated by means of bond strength test. The concretes dealt with this study were produced by two different cold bonding fly ash lightweight coarse aggregate contents. The LWAC with constant water-to-cement ratio of 0.4 and 400kg/m3 cement content were designed. Three types of hooked-end steel fibers with the aspect ratios of 55, 65, and 80 were utilized with four different volume fractions of 0.35%, 0.70%, 1.00%, and 1.50% of concrete volume. The effectiveness of aspect ratio, steel fiber volume fraction, and lightweight aggregate content on the bond strength were investigated at the end of 28-days of water curing. Analyses of variance on the experimental data were performed and the levels of the significance of the lightweight aggregate content, steel fiber aspect ratio and volume fraction on the bond strength of the concretes were evaluated through general linear model analysis of variance (GLM-ANOVA). Furthermore, a mathematical model was proposed for predicting the bond strength of the concretes dealt with the current study. The results revealed that utilization of steel fiber enhanced the bond strength and the ductility of pull-out failure. Moreover, the bond strength was significantly affected by the artificial fly ash lightweight aggregate content.

Water absorption, permeability, and resistance to chloride-ion penetration of lightweight aggregate concrete

This paper presents an experimental study to evaluate effect of cumulative lightweight aggregate (LWA) content (including lightweight sand) in concrete [water/cement ratio ( w/ c) = 0.38] on its water absorption, water permeability, and resistance to chloride-ion penetration. Rapid chloride penetrability test (ASTM C 1202), rapid migration test (NT Build 492), and salt ponding test (AASHTO T 259) were conducted to evaluate the concrete resistance to chloride-ion penetration. The results were compared with those of a cement paste and a control normal weight aggregate concrete (NWAC) with the same w/ c and a NWAC (w/ c = 0.54) with 28-day compressive strength similar to some of the lightweight aggregate concrete (LWAC). Results indicate that although the total charge passed, migration coefficient, and diffusion coefficient of the LWAC were not significantly different from those of NWAC with the same w/ c of 0.38, resistance of the LWAC to chloride penetration decreased with increase in the cumulative LWA content in the concretes. The water penetration depth under pressure and water sorptivity showed, in general, similar trends. The LWAC with only coarse LWA had similar water sorptivity, water permeability coefficient, and resistance to chloride-ion penetration compared to NWAC with similar w/ c. The LWAC had lower water sorptivity, water permeability and higher resistance to chloride-ion penetration than the NWAC with similar 28-day strength but higher w/ c. Both the NWAC and LWAC had lower sorptivity and higher resistance to chloride-ion penetration than the cement paste with similar w/ c.