•Softening effect is an inherent property of porous media materials.•LWAC has a softening effect because of the same feature of the LWA itself and the complex effect of pore water.•The ultimate ...compressive strength σ30 at the confining pressure σc = 0 can be used as σ0 to replace the axial compressive strength fc, thereby significantly improving the calculation accuracy of the corresponding criterion.•The calculation method and compatibility judgement condition of six characteristic test points of concrete are given.
Softening effect refers to the inherent property of porous media materials of having their strength decrease over time under water saturation compared with that under dry condition. Typical porous media materials, such as ceramsite and ceramsite-based concrete, exhibit a softening effect. This study investigated the softening effect of shale ceramsite (SC) and different types of lightweight aggregate concrete (LWACs). Mix ratios of LC30 all-lightweight shale ceramsite concrete (also known as all-lightweight concrete, ALWC) whose SC and shale pottery (SP) were selectively or simultaneously replaced with limestone gravel (LSG) and river sand (RS) with the same volume fraction, respectively, were prepared for comparison with gravel lightweight concrete (GLWC), sand lightweight concrete (SLWC) and hybrid aggregate lightweight concrete (HALWC) were formed. The four kinds of LWACs (ALWC, GLWC, SLWC and HALWC) were cast into their corresponding specification and size specimens and demoulded after indoor curing for 24 h, with their target ages (7–180 d) maintained under standard and hydrostatic curing. Then, the strength and initial elastic modulus under uniaxial stress, ultimate compressive strength and stress–strain curves under triaxial stress of the specimens were tested to analyse the influence of aggregate types and curing methods on the mechanical properties and softening effect of LWACs. According to the test results, the cube compression, prism compression, splitting tensile, conventional triaxial compression and elastic modulus decreased after 180 d of hydrostatic curing; the experimental age of the conventional triaxial compression test was after 90 d. ALWC demonstrated the most evident decrease, followed by SLWC, HALWC and GLWC. The trend indicates that normal aggregates can significantly improve the softening effect of LWACs. The failure modes of the triaxial compression specimens changed from splitting failure to shear failure, and a plastic platform phenomenon was apparent on the stress–strain curves, with their descending section appearing gentler than those in the uniaxial compression test with the increase in confining pressure. The relationship between ultimate compressive strength and confining pressure of the LWACs can be accurately described by the Mohr–Coulomb single-parameter failure criterion, Hsieh–Ting–Chen four-parameter failure criterion and Willam–Warnke five-parameter failure criterion. However, the three failure criteria demonstrated application limitations based on meridian equation and deviatoric plane analysis. The extension trend of the compression meridian of the LWACs after 90 d of hydrostatic curing was generally the same, and the types of aggregates exerted a minimal effect on the meridian and deviatoric plane limit trace. The softening effect of LWACs was mainly caused by the softening effect of the SC itself and the influence of pore water on the matrix concrete.
This study presents a comparative analysis of the effects of lightweight aggregate concrete (LWAC) and foamed concrete (FC), with dry densities of 500, 750 and 1000 kg/m3, on the thermal performance ...of a typical multi-family (residential) building. Typical two-layer walls consisting of an essential layer (LWAC or FC), with an insulating layer of foamed polystyrene were evaluated. To ensure fixed U values for all variants tested, the thicknesses of the support layers were adjusted accordingly, in such a way that in each variant the load-bearing layer had the same value of the thermal resistance, thus ensuring the same thermal transmittance value for the entire wall. Calculations were made for four different climate zones, making it possible to determine the impact of each variant used, in different climatic conditions. For a hot climate, the data for Cairo (Egypt) was used. A moderate, warm climate was represented by Vienna (Austria), a moderate cold climate by Kołobrzeg (Poland) and a cold climate by Tromsoe (Norway). Significant correlations between the type/density of concrete and climate zones were established. The study shows that, despite comparable densities and thermal conductivity values between LWAC and FC, their specific heat and thus dynamic thermal properties are different. Study provides valuable guidelines and knowledge on choice between proper lightweight concrete type depending on the climate zone. Meaningful conclusions were drawn, showing that the pursue for developing the material with “the lowest” thermal conductivity itself is not the key factor to develop a residential building with satisfactory thermal comfort.
•LWAC and FC with densities of 500, 750, and 1000 kg/m3 were used as a structural layer of wall for typical multi-family building model.•144 variants including 4 locations, 3 ventilation rates, 2 cooling system variants were simulated.•Higher specific heat values of LWAC than FC affects positively both thermal admittance and internal heat capacity.•In hot and mild warm climates, thinner walls with lower thermal conductivity reduced the number of hours exceeding internal temperatures.•The use of thicker wall layers with higher thermal conductivity reduces the heating demand in cold and moderate climates.
•Microstructure in the ITZ of lightweight concretes was studied.•Lightweight aggregates (LWA) contributed to the formation of a dense and thinner ITZ.•Lightweight structural concretes were developed ...and explained.
In this research both the microstructure and thickness of the interfacial transition zone (ITZ) in concretes of Portland cement and lightweight aggregates (LWA) are studied. It has been established that the microstructure in the ITZ strongly depends on the nature of the aggregate, specifically its porosity and water absorption. This study aims at researching the influence of physical properties such as density, porosity and morphology of lightweight aggregates such as pumice and expanded clays, on the microstructure and thickness of ITZ, and determine the effect that these factors have in turn on the mechanical properties as compressive strength of lightweight concretes (LWC). Lightweight aggregates were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and X-ray Fluorescence (XRF), to determine their mineralogical, morphological and chemical characteristics. The characterization of ITZ by SEM-EDS, and conventional optical microscopy, was carried out on specimens of concrete manufactured with LWA and with a conventional aggregate, in order to evaluate its thickness; furthermore, to determine the porosity, digital image processing (DIP) was performed. Lightweight aggregates contributed to the formation of a dense and thinner ITZ, when compare to the ITZ of a conventional concrete. The lower porosity and greater amount of hydrated cement phases in the ITZ of lightweight aggregates are attributed to their physical, morphological properties and chemical and mineralogical composition; which contributed to the decrease of the wall effect, gestating from its surface the formation of C-S-H, achieving interlacing of hydrated phases on the surface of these aggregates with the cementitious matrix.
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•An extensive review on the behavior of aerogel based cementitious composites.•Significant improvement in thermal insulation performance.•Satisfactory results of compressive strength ...specimens with 60 vol% aerogel.•A decrease in U-values was observed for aerogel based thermal insulating products.•Pretreatment by silane coupling agent can improve the consequences of silica aerogel.
With the increase in global warming, the demand for more sustainable and thermal insulating cement-based lightweight composite increases. From the past few decades, researchers worldwide have carried out extensive research on lightweight concrete using various lightweight aggregates. The use of aerogel as an aggregate in lightweight concrete is the most promising building application these days. With the exceptional characteristics of thermal insulation, ultra-low density, high adsorption, high surface area, aerogel shows a remarkable behavior. Although, the poor mechanical characteristics and high cost of aerogel have negative effects on the aerogel-incorporated concrete. This article is aimed to present a complete in-depth review of aerogel incorporated cementitious materials in terms of production/synthetisation, fresh rheology and proportioning, mechanical, microstructural, and durability properties, including water absorption, capillary water absorption, fire resistance, and exposure to elevated temperature, thermal insulation properties, and economic perspectives of aerogel. Particular emphasis has been given to study the hygrothermal behavior of aerogel-based cement composites. In addition, the present investigation gives a summary of case studies that have been performed for aerogel-based cementitious products used in buildings. The study suggests the promising future of aerogel as lightweight thermal insulating composites with sufficient mechanical properties.
In this paper the main mechanical properties of concrete produced with recycled aggregates obtained from crushing both structural and non-structural lightweight concrete are characterized. Various ...concrete mixes with replacement ratios of 20%, 50% and 100% of two types of coarse lightweight aggregates (LWA) by recycled lightweight concrete aggregates (RLCA) were studied in terms of their compressive strength, tensile strength, modulus of elasticity and abrasion resistance. Generally the experimental results show that all the studied properties are improved with the introduction of RLCA. In particular, concrete with RLCA has higher structural efficiency than the reference concrete, with LWA alone. It is thus concluded that more cost-effective structural lightweight concrete (LWC) can be produced with the introduction of RLCA. Moreover, it is shown that the RLCA obtained from non-structural lightweight concrete can be used to produce structural LWC. There is a slight reduction of the concrete's mechanical properties when the stronger LWA is replaced with the more porous RLCA obtained from non-structural lightweight concrete.
Research in Iraq has expanded in the field of material technology involving the properties of the lightweight concrete using natural aggregate. The use of the porcelinate aggregate in the production ...of structural light concrete has a wide objective and requires a lot of research to become suitable for practical application. In this work metakaolin was used to improve compressive strength of lightweight porcelinate concrete which usually have a low compressive strength about 17 MPa . The effect of metakaolin on compressive, splitting tensile, flexure strengths and modulus of elasticity of lightweight porcelinate concrete have been investigated. Many experiments were carried out by replacing cement with different percentages of metakaolin. The metakaolin was replaced by 5%, 10%, 15% and 20%. A control reference mix without metakaolin was made for comparison purpose. For all mixes, compressive, splitting tensile, flexure strengths and modulus of elasticity were determined at 28-day. The results showed that the using of metakaolin improve the compressive, splitting tensile, flexure strengths and modulus of elasticity of lightweight porcelinate concrete. The higher compressive, splitting tensile, flexure strengths and modulus of elasticity were found for 15% metakaolin.
In this investigation, agro-solid waste materials from the palm oil industry such as oil palm shell (OPS) and palm oil fuel ash (POFA) were utilized to replace conventional concrete-making materials ...to produce lightweight concrete. The OPS was used as replacement for conventional coarse aggregate while ground POFA was used at partial cement replacement levels of up to 25%. The inclusion of POFA up to 25% did not detrimentally affect the fresh concrete properties while the use of POFA at 10–15% replacement levels improved the compressive strength of OPS concrete (OPSC). Although there was little effect of POFA on the modulus of elasticity, increased POFA replacement levels led to reduction in both the splitting and flexural tensile strengths of OPSC. The evaluation of the cost and eco-efficiencies showed that inclusion of 10% POFA gave the most optimum performance in terms of the sustainability of the OPSC.
•The development of recent design codes for two-way shear of LWC slabs was outlined.•An extensive review for five decades of experimental testing of LWC slabs under two-way shear was conducted.•A ...Comparative study between selected recent design codes for LWC slabs under two-way shear was outlined and discussed.•The effect of various parameter on the two-way shear design of LWC slabs was investigated and discussed.•A physically sound, simple, and accurate model is proposed.
Developing design models that are accurate compared to experimentally measured strength, yet physically sound, continues to be the ultimate research goal. For this purpose, the two-way shear design provisions of the American design codes have been updated. While that of the European design codes are being investigated. The two-way shear failure of slabs is a sudden one, which can be catastrophic. In addition, lightweight concrete (LWC) is gaining a lot of attention due to its economic advantage, however, very limited studies focus on investigating LWC slabs under two-way shear loading. The purpose of this study is to examine existing design codes and ongoing proposals for the case of LWC slabs under two-way shear. A comprehensive literature review of the available two-way shear testing for LWC slabs was conducted. An extensive database with a total of 129 tested LWC slabs was compiled. Selected design codes were used to calculate the two-way shear strength of the tested slabs. The Strength ratio (SR) was compared for selected codes, which is calculated as the ratio between the experimentally measured strength and that calculated using different design codes. In addition, the effect of various parameters on the SR was assessed. Concluding remarks were outlined and discussed. Moreover, a design formula for LWC slabs under two-way shear, which is physically sound and simple was developed and validated using experimental results. It was found to be more accurate, and more consistent compared to existing design codes with regard to experimentally measured strength. It is worth noting, that the investigated draft of the Eurocode is not final. However, these findings could help develop future design provisions for two-way shear of LWC slabs, which have to be physically sound, more consistent, and more accurate compared to existing one.
•Lightweight EPS concrete was produced by partially replacing EPS beads with foams.•A noval method to evaluate homogeneity of concrete during setting was developed.•Segregation of EPS concrete was ...significantly reduced at an optimum foam content.•Strength of EPS concrete was enhanced by introduction of a proper amount of foam.•EPS foamed concrete is ductile and exhibits a high energy absorption capacity.
The main objective of this study is to provide additional data on the effects of foam content on the workability, mechanical properties and thermal conductivity of EPS (expanded polystyrene) foamed concrete. In the experimental studies, mixtures were prepared by partially replacing EPS beads with foam with a bubble diameter of 25–100μm; the resulting densities of the EPS foamed concretes in a fresh state were 400kg/m3 and 800kg/m3. The test results show that proper foam content introduced into the EPS mixture can greatly improve the workability, strength and thermal conductivity of EPS foamed concrete. Novel lightweight EPS concretes with densities 400kg/m3 and 800kg/m3 were produced, with strengths of 3.0MPa and 0.009W/mk, respectively, and thermal conductivities of 13.0MPa and 0.25W/mk, respectively. The recorded stress–strain curves of the material indicated that EPS foamed concrete is ductile. Moreover, EPS foamed concrete is capable of retaining the load after ultimate stress and has a high energy absorption capacity under compressive load.
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