Failure Criteria and Constitutive Relationship of Lightweight Aggregate Concrete under Triaxial Compression

This paper investigates the compression behavior and failure criteria of lightweight aggregate concrete (LAC) under triaxial loading. A total of 156 specimens were tested for three parameters: concrete strength, lateral confining pressure and aggregate immersion time, and their effects on the failure mode of LAC and the triaxial stress-strain relationship of LAC is studied. The research indicated that, as the lateral constraint of the specimen increases, the failure patterns change from vertical splitting failure to oblique shearing failure and then to indistinct traces of damage. The stress-strain curve of LAC specimens has an obvious stress plateau, and the curve no longer appears downward when the confining pressure exceeds 12 MPa. According to the experimental phenomenon and test data, the failure criterion was examined on the Mohr–Coulomb theory, octahedral shear stress theory and Rendulic plane stress theory, which well reflects the behavior of LAC under triaxial compression. For the convenience of analysis and application, the stress-strain constitutive models of LAC under triaxial compression are recommended, and these models correlate well with the test results.

Preparation of Lightweight Ceramsite from Solid Waste Using SiC as a Foaming Agent

SiC was chosen as the foaming agent, and river bottom silt, waste oil sludge, paint bucket slag, and fly ash were used as raw materials, to prepare lightweight ceramsite without adding any chemical additives. The effects of SiC dosing and sintering temperature on various properties of the ceramsite were studied, and the pore-forming mechanism of the lightweight ceramsite was clarified by thermal analysis and X-ray diffraction analysis. The results showed that the single ceramsite compressive strength, water absorption, bulk density, and porosity of ceramsite sintered at 1180 °C with 1.0% SiC were 2.15 MPa, 2.02%, 490 kg/m3, and 23.85%, respectively. The major mineralogical compositions were quartz, fayalite, and kyanite, with small amounts of albite-low from 1140 to 1190 °C. Furthermore, the concentration of all tested heavy metals from ceramsite was lower than the maximum allowable concentration of the leaching solution specified in the Chinese national standard (GB 5085.3-2007), which reveals that this solid waste ceramsite will not cause secondary environmental pollution. The prepared ceramsite, exhibiting lower bulk density, high water absorption and porosity, and effective solidification of deleterious elements, can be used to prepare green lightweight aggregate concrete. Importantly, preparation of solid waste ceramsite is an effective way to dispose of hazardous wastes.

Industrial Wastes-Cum-Strength Enhancing Additives Incorporated Lightweight Aggregate Concrete (LWAC) for Energy Efficient Building: A Comprehensive Review

Lightweight aggregate concrete (LWAC) exhibits the advantages of thermal insulation, reduces energy consumption building costs, improves building efficiency and easy construction. Furthermore, the utilization of industrial wastes in concrete is advantageous in terms of environmental sustainability. In order to explore this, several researchers investigated the idea of integrating industrial wastes in LWAC. However, the lack of knowledge regarding the performance of industrial waste-based lightweight aggregate concrete hinders the adaptation of this concept and application of LWAC in the construction sector. Therefore, this paper summarizes the research in relation to the sustainable LWACs containing oil palm shell (OPS), lightweight expanded clay aggregate (LECA), vermiculite, perlite, pumice and sintered fly ash as lightweight aggregate, along with industrial wastes and strength-enhancing additives (viz. fibers, polymers, etc.). Firstly, desirable physical, chemical, morphological and mineralogical characterization of different lightweight aggregates are presented, and then a comprehensive overview on fresh, hardened, durability and thermal properties of LWAC incorporating industrial wastes are discussed in comparison with normal weight concrete. The review also highlights the current challenges and suggests the research gaps for further development of eco-friendly LWAC. It is concluded that vermiculite, perlite, pumice, OPS, sintered fly ash and LECA with some suitable industrial waste materials have the potential to be used in the construction sector. Moreover, LWAC with industrial waste has 50–65% lower carbon emission (kg CO2 eq/m3) in the environment. The scientific contribution of this paper provides insights into different LWACs and the knowledge base for future research and paradigm shift of using LWACs as more common alternative building materials.

Dynamic Properties Test and Constitutive Relation Study of Lightweight Aggregate Concrete under Uniaxial Compression

For the purpose of studying the dynamic properties of lightweight aggregate concrete, dynamic performance tests under uniaxial compression were conducted by considering 10 different strain rates ranging from 10−5/s to 10−1/s, from which the stress-strain curves under various compressive loads were obtained. From the stress-strain curves, parameters including peak stress, peak strain, and elastic modulus of lightweight aggregate concrete, as well as the concrete failure mode, were determined and examined. By reviewing the relevant literature on ordinary concrete, the dynamic properties of lightweight aggregate concrete were analyzed accordingly. Meanwhile, by applying the dynamic elastoplastic damage constitutive model, the effect of dynamic rate on lightweight aggregate concrete was calculated. The experimental results showed that the damage mode of lightweight aggregate concrete under the static and dynamic strain rates belonged to shear failure, which is different from that of ordinary concrete (binding material failure). On the other hand, it was also found that the peak stress and elastic modulus of lightweight aggregate concrete could be increased by 54.48% and 28.75%, respectively, with the increase of strain rate, suggesting that the loading strain rate has a stronger influence on lightweight aggregate concrete than on ordinary concrete. Based on the experimental data, both the peak stress and nondimensionalized elastic modulus are in linear relationship with the logarithm of the nondimensionalized strain rate. Moreover, the established constitutive model had been verified as an effective and reliable tool for simulating the dynamic rate effect of lightweight aggregate concrete.

Ductility and flexure of lightweight expanded clay basalt fiber reinforced concrete slab

Relevance. The load on a reinforced concrete slab with high strength lightweight aggregate concrete leads to increased brittleness and contributes to large deflection or flexure of slabs. The addition of fibers to the concrete mix can improve its mechanical properties including flexure, deformation, toughness, ductility, and cracks. The aims of this work are to investigate the flexure and ductility of lightweight expanded clay concrete slabs reinforced with basalt fiber polymers, and to check the effects of basalt fiber mesh on the ductility and flexure. Methods. The ductility and flexural/deflection tests were done on nine engineered cementitious composite (expanded clay concrete) slabs with dimensions length 1500 mm, width 500 mm, thickness 65 mm. These nine slabs are divided in three reinforcement methods types: three lightweight expanded clay concrete slab reinforced with basalt rebars 10 mm (first slab type); three lightweight expanded clay concrete slab reinforced with basalt rebars 10 mm plus dispersed chopped basalt fiber plus basalt fiber polymer (mesh) of cells 2525 mm (second slab type); three lightweight expanded clay concrete slab reinforced with basalt rebars 10 mm plus dispersed basalt fiber of length 20 mm, diameter 15 m (third slab type). The results obtained showed physical deflection of the three types of slab with cracks. The maximum flexural load for first slab type is 16.2 KN with 8,075 mm deflection, second slab type is 24.7 KN with 17,26 mm deflection and third slab type 3 is 32 KN with 15,29 mm deflection. The ductility of the concrete slab improved with the addition of dispersed chopped basalt fiber and basalt mesh.