Addition Of Lightweight Aggregates Research Articles

Mechanical properties and cracking behaviour of lightweight engineered geopolymer composites with fly ash cenospheres

Engineered geopolymer composites (EGCs) are known for their superior tensile performance and multiple cracking characteristics. The development of lightweight EGCs is crucial for applications in structural strengthening and repair. However, the addition of lightweight aggregates often compromises the mechanical properties of these composites. Fly ash cenosphere (FAC) has demonstrated its effectiveness as an aluminosilicate precursor in geopolymers and as a crack width controller in fibre-reinforced cementitious composites, thus showcasing significant potential for the advancement of high-performance lightweight EGCs. This study investigates the effects of FAC incorporation on the properties of lightweight EGCs. The results of this study confirmed the benefits of using FACs in terms of reducing the density of the composites while maintaining satisfactory compressive strength. With increasing the FAC replacement ratio, the tensile strength decreases; however, increasing the FACs/binder ratio preserves the tensile strength of the EGCs. Moreover, the utilisation of FACs preserves the high tensile strain capacity of lightweight EGCs, reaching approximately 9 %. Furthermore, the presence of fractured unreacted FACs, partially hollow reacted FACs, and a weak FAC/geopolymer interface act as artificial flaws, thereby enhancing the crack control ability of EGCs with higher FAC replacement or FACs/binder ratios. Moreover, the inclusion of FACs does not alter the main reaction products of EGCs, providing an attractive avenue for achieving lightweight EGCs with exceptional tensile strain capacity.

Experimental studies on behavior of hybrid materials concrete using non-destructive testing (NDT) methods

This paper presents the experimental studies conducted on hybrid materials concrete using non-destructive testing (NDT) methods. M−35 grade hybrid concrete was designed by incorporating Fly ash and Alccofine in the ratios of 5 %, 10 % and 15 % as a partial replacements to cement. Further, light weight aggregates were used to partially replace the natural coarse aggregates in the ratios of 5 %, 10 % and 15 %. A cumulative of 13 concrete mixes were prepared to investigate the behavior of hybrid materials concrete under different NDT methods. Ultra-sonic Pulse velocity (UPV) testing was conducted on 150 mm concrete cube specimens in three different conditions, namely direct UPV, semi-direct UPV and indirect UPV. Rebound hammer (RH) test was also performed to study the strength of concrete. The results of concrete under NDT testing were then validated by comparing them with compressive strength values. The experimental results showed that, the increase in fly ash content moderately improved the compressive strength of concrete and the addition of light weight aggregates decreased the compressive strength of concrete. The alccofine addition to concrete has yielded higher compressive strength and better NDT values of concrete. A maximum compressive strength of 45.54 MPa was obtained with 15 % alccofine replacement. The hybrid concrete containing 5 % light weight aggregates, 15 % alccofine and 10 % fly ash yielded a compressive strength of 42.68 MPa, which is 17 % higher than the reference mix. The values obtained from NDT methods were in good agreement with the compressive strength values. The results were also used to develop statistical models and the numerical equations were established for compressive strength in terms of percentage replacement of constituent materials.

Study of the influence of the addition of closed- structure expanded perlite microspheres on the density and compressive strength of cement pastes

The current trend in the construction industry is the development of ever lighter-weight elements and components that can maintain the good mechanical properties of traditional construction materials. The addition of lightweight aggregates, including expanded perlite, in concrete is one of the most common techniques used for density reduction of cementitious products. Nevertheless, one of the main drawbacks attributed to conventional expanded perlite, which affects the final product properties, is the increased water absorption that this material exhibits due to its high porosity.Expanded perlite microspheres (EPMs) is a novel, low cost material that uniquely combine important properties rendering it an ideal filler; it is micro-sized, spherical, inert, lightweight, thermal insulating, with closed external surface and considerable mechanical properties. 4 EPM grades of different density (67 to 233 kg·m3) were produced through indirect heating using a Vertical Electric Furnace (VEF) and were incorporated in cement pastes. The addition level (0.0–0.4 ml perlite/g cement) of each perlite quality in cement pastes with w/c ratio of 0.35 was investigated through the analysis and evaluation of the density and compressive strength of the final cementitious products. SEM/EDS measurements were performed on selected samples, in order to evaluate the microstructure of the developed products, which is known to affect their mechanical properties.In the present study, the effect of the EPM properties (expansion degree, porosity, morphology and strength) and quantity, on the density, compressive strength and morphology of the final cementitious composite was investigated.

Segmentação de imagens microtomográficas tridimensionais de concretos leves usando técnicas de limiarização automática para cálculo de porosidade aparente

Construction industry demands sustainable processes and the addition of lightweight aggregates presents as an effective solution to obtain different concrete mixtures by recycling production outputs from other industries, as the Ethylene-Vinyl Acetate (EVA), raw material mostly utilized at footwear industry. Despite all the sustainable appeal in the recycle of EVA or other lightweight aggregates into the concrete mixtures, the loss of resistance is a frequent issue that can be prevented by adding natural fibers, such as piaçava, to the composition. Aiming the usage of these new materials, it is necessary to know their characteristics. In materials science the techniques of non-destructive tests stand out for maintaining the integrity of the material in question promoting savings and sustainability. In this work, X-ray computerized microtomographic images from samples of different lightweight concrete compositions were analyzed. These analyzes were carried out by image processing techniques, such as the Otsu and k-means, aiming to characterize the microstructure of the cementitious matrix of lightweight concrete mixture with EVA and piaçava fiber. The three-dimensional analysis of the microtomographic images offers descriptors that make it possible to characterize these samples. The results were satisfactory when compared with mercury porosimetry tests performed on the samples.

Surface hydrophobisation of mortars with waste aggregate by nanopolymer trietoxi-isobutyl-silane and methyl silicon resin

The paper explores the possibility of applying the nanopolymer trietoxiisobutylsilane and methyl silicon resin for hydrophobisation of mortars with the lightweight aggregate addition (PVC + PUR + WD). The investigation involved the mortars with two types of hydrophobic agents, without and with waste addition (5; 10; 15%). The results and discussion referring to their micro-structure together with the interfacial transition zone (ITZ). Physical and mechanical properties, frost resistance, water absorption, as well as vapor permeability were investigated. The influence of hydrophobisation on the SFE value, CA and microroughness characteristic was also determined. The surface hydrophobisation of mortars using the A1 preparation reduced the water absorption and vapour permeability by 94.6%. The A1 agent reduced the weight loss after the F-T test by 88.9%. Surface hydrophobisation increased the CA value, and reduced the SFE value for the L5 and L10 mortars by over 3 times. The greatest effect on the decrease of A2 preparation roughness was proven. The efficiency of both agents was confirmed by the capillary uptake test conducted using the TDR equipment.

Effects of Presoaked Lightweight Aggregate Addition on Drying Shrinkage

AbstractIt is widely known that presoaked lightweight aggregate (LWA) is greatly beneficial for reducing autogenous shrinkage by providing additional water reservoirs for the mixture. However, in u...

Preparation and Characterization of Ultra-Lightweight Foamed Concrete Incorporating Lightweight Aggregates

Increasing interest is nowadays being paid to improving the thermal insulation of buildings in order to save energy and reduce ecological problems. Foamed concrete has unique characteristics and considerable potential as a promising material in construction applications. It is produced with a wide range of dry densities, between 600 and 1600 kg/m3. However, at a low density below 500 kg/m3, it tends to be unstable in its fresh state while exhibiting high drying shrinkage in its hardened state. In this study, lightweight aggregate-foamed concrete mixtures were prepared by the addition of preformed foam to a cement paste and aggregate. The focus of the research is the influence of fly ash, as well as fine lightweight aggregate addition, on the properties of foamed concrete with a density lower than 500 kg/m3. Concrete properties, including stability and consistency in the fresh state as well as thermal conductivity and mechanical properties in the hardened state, were evaluated in this study. Scanning electron microscopy (SEM) was used to study the microstructure of the foamed concrete. Several mixes with the same density were prepared and tested. The experimental results showed that under the same bulk density, incorporation of fine lightweight aggregate has a significant role on compressive strength development, depending on the characteristics of the lightweight aggregate. However, thermal conductivity is primarily related to the dry density of foamed concrete and only secondarily related to the aggregate content. In addition, the use of fine lightweight aggregate significantly reduces the drying shrinkage of foamed concrete. The results achieved in this work indicate the important role of lightweight aggregate on the stability of low-density foamed concrete, in both fresh and hardened states.

Assessing and understanding the interaction between mechanical and thermal properties in concrete for developing a structural and insulating material

Highly thermal insulated building envelopes are the base of energy efficient buildings worldwide, however, concrete show poor thermal insulation properties. Developing a structural and thermal insulating concrete is challenging because improving thermal properties undermines mechanical properties. This study aims to understand the interactions between thermal and mechanical properties of concrete (conductivity-to-strength efficiency), when modifying the matrix and aggregate phases by adding fly ash (FA) and coarse and fine lightweight aggregates (LWAs). Based on the ratio fc/λ, the highest efficiency was given by the addition of LWAs (0.017 [W/mK]/MPa) in comparison with the addition of FA (0.008 [W/mK]/MPa). Nevertheless, those efficiencies are highly dependent on the interaction between the aggregate and matrix phases. The optimization of one phase only is not enough to obtain a structural insulating concrete because the thermal conductivity-to-strength efficiency is governed by both, the aggregate and the matrix.

Failure Mechanism of Foamed Concrete Made with/without Additives and Lightweight Aggregate

It has been reported that owing to a densification of the internal structure of concrete, adding mineral admixtures leads to a more brittle behaviour. Therefore, with the intention of modifying (increasing the strength of) foamed concrete to make it suitable for structural purposes by means of admixtures and lightweight aggregate addition, the effect of these additions on the failure mechanism under compressive and tensile loading using different techniques is evaluated and discussed in this paper. Eight different mixes, made using a pre-formed foam, were investigated with varying density (different foam volumes), nominally 1300, 1600 and 1900 kg/m3, without/with admixtures (silica fume, fly ash and superplasticizer) and lightweight aggregate. The Digital Image Correlation (DIC) technique was adopted to measure the deformations and strains on the surface of a specimen under uniaxial compressive load. Meanwhile, a Video Gauge technique was used to measure the horizontal deformation of discs during a splitting tensile test. From elasticity, fracture and fractal points of view, it was found that, for the same density, brittleness increases with many of the additives while it reduces with inclusion of lightweight aggregate. However, for all mixes, the lower the density (higher added foam volume), the higher the ductility.

Simulation of moisture field of concrete with pre-soaked lightweight aggregate addition

Use of pre-soaked lightweight aggregate (PSLWA) as an internal reservoir to provide water as the concrete dries is an effective method to reduce shrinkage of concrete. In this paper, a moisture distribution model of concrete internal cured with PSLWA is developed based on the experimental measurement on internal relative humidity of concrete with and without internal curing under sealing status. The function of internal curing with PSLWA is considered in the model through a parameter called critically released water, Wc, that was experimentally determined from experiments. Meanwhile, self-desiccation and moisture capacity are taken into account in development of the diffusion equation. To verify the model, a series tests to measure the internal relative humidity of three kinds of internal cured concrete under drying and sealing conditions were conducted. Through comparing the model and test results of humidity profiles, the moisture dependent diffusivity of the three internal cured concretes is obtained. The developed moisture movement model and finite differential method can well predict the moisture distribution as well as its variations with time of concrete internal cured with PSLWA.

Self-compacting lightweight aggregate concrete: design and experimental study

This study focuses on the production of self-compacted lightweight structural concrete. For this purpose, lightweight concrete was produced by replacing normal aggregate with pumice aggregate obtained from the Kayseri region. Three series of mixtures were prepared to obtain the proper self-compacting lightweight concrete (SCLC) mixture. The D series included normal-weight, self-compacting concrete (SCC) mixtures and the H series included SCLC mixtures having 100% lightweight coarse aggregate and different air contents. Fresh concrete test results obtained from these mixtures were used as a basis for the T series containing different amounts of lightweight and normal-weight coarse aggregate. Some mechanical and fresh concrete properties were obtained from the T series. It was found that the loss of strength owing to lightweight aggregate addition is higher than the decrease of unit weight of the mixture. Furthermore, the decrease in flexural tensile strength owing to addition of lightweight aggregate is less than the reduction in compressive strength and splitting tensile strength. The percentage of entrained air and paste content are important factors to avoid segregation problems in lightweight SCC mixtures. There is a good relationship between 28-day compressive strength and unit weight data obtained from the H and T series.

Internal curing of mortars by lightweight aggregates and its effects on hydration

This study investigates the effects of lightweight aggregates (LWAs) on heat and degree of hydration in high-strength cementitious materials, in which natural pumice LWAs were used as water reservoirs to provide internal curing for mitigating autogenous deformation. Normal aggregates were substituted by LWAs at three different volume fractions, such as 8%, 16%, and 24% of total volume of mortars. The results show that as the amount of LWAs increased, the autogenous deformation significantly decreased, while the heat of hydration increased slightly. The cement particles can easily find water released from LWAs and consequently, the degree of hydration increased due to internal curing. The addition of LWAs caused a delay in the time to approximately reach the asymptotic value of the nonevaporable water content.