International Concrete Abstracts Portal

The apparent density of lightweight aggregate (LWA)-modified ultra-high-performance concrete composite is 2080 kg/m3, and the compressive strength is not less than 110 MPa at 28 days. Lightweight ultra-high-performance concrete (LUHPC) not only has light weight and high strength, but also reduces the consumption of raw materials and the section size of the structure, thus reducing the cost. The macroscopic properties are closely related to the pore structure characteristics, but the structural nature of LUHPC under different curing regimes and the LWA on their pore structure remain unclear. To comprehensively understand the pore structure of LUHPC and then control its properties, capillary absorption method, low-field nuclear magnetic resonance (LF-NMR), computed tomography (CT), and nitrogen adsorption (BET) technologies were used to characterize the pore structure characteristics of LUHPC. The experimental results show that there are many nanoscale pores (mainly harmful and more-harmful pores) in LUHPC. With the increase of water absorption of the added LWA, the porosity of LUHPC and the proportion of less-harmful pores increase, thus changing the pore structure of LUHPC. With the increase of temperature and pressure, the internal curing effect of LWA is accelerated. Heat treatment promotes the formation of dense additional hydrates such as tobermorite and xonotlite, and the average chain length of the hydrates and the pozzolanic reaction between supplementary cementitious material and Ca(OH)2. Steam curing increases the total porosity and coarsens the pore size while accelerating the hydration of cementitious paste. Autoclaved curing can stimulate the pozzolanic activity of inert SiO2, promote the formation of secondary hydration products, and fill the pores in the matrix. The evolution of the pore structure of LUHPC plays a key role in improving its performance due to the curing regimes and presence of LWA.

Based on the unified strength theory as the yield criterion, an elastic-plastic constitutive model of autoclaved aerated concrete block (AACB) considering the intermediate principal stress was proposed. Meanwhile, the mechanical properties and failure mechanism of AACB were investigated by the uniaxial compressive, tensile, shear, and static triaxial compressive tests. The yield function based on the unified strength theory of AACB was derived. Moreover, the proposed model was integrated into the general finite element package ABAQUS by UMAT to simulate the deformation process of AACB under triaxial compressive. The numerical simulation results of AACB were in good accordance with but slightly larger than the static triaxial test results, which implied that the proposed constitutive model could be used to characterize the mechanical characteristics of AACB under complex stress states with high computational efficiency.

An optimum mixture proportion design method of reactive powder concrete (RPC) based on an artificial neural network (ANN) and harmony search (HS) algorithm was developed. ANNs were adopted to establish the relationship between design parameters (water-binder ratio, silica fume content, sand-binder ratio, and steel fiber content) and properties (compressive strength under standard curing and autoclaved curing, splitting tensile strength under autoclaved curing, and slump) of RPC, and the HS algorithm was used to design and optimize RPC mixture proportions with the objective criterion of minimum cost while meeting all property requirements. The proposed method can consider the influence of curing regimes, and its reliability was verified by experiment data.

Coal fly ash, a by-product of coal combustion in thermal power plants, is one of the most complex and abundant anthropogenic materials. For several years, siliceous fly ash has been predominantly used as a substitute for material in the construction industry, either as a raw material or as an additive in the cement industry all over the world. Fly ash produced in coal-fired plants based on fluidized bed combustion technology accompanied by in-furnace desulfurization has significantly different properties compared to siliceous ashes. In this study, a brief characterization of fly ash from fluidized bed boilers is presented and possible alterations in fly ash use in autoclaved concrete production are discussed. Autoclaved aerated concrete production involving fluidized ashes proved to be more cost-effective and environmentally friendly. The content of lime and sulfates was found to be reduced by 10% to 20% and 60% to 100%, respectively, which limited the exploitation and consumption of the natural raw materials.

The low velocity impact response of plain autoclaved aerated concrete (AAC) and carbon fiber reinforced polymer (CFRP)AAC sandwich panels has been investigated. The structural sandwich panels composed of CFRPAAC combinations have shown excel¬lent characteristics in terms of high strength and high stiffness-to-weight ratios. In addition to having adequate flexural and shear properties, the behavior of CFRPAAC sandwich panels needs to be investigated when subjected to impact loading. During service, the structural members in building structures are subject to impact loading that varies from object-caused impacts, blasts due to explo¬sions, and high-velocity impact of debris during tornados, hurri¬canes, and storms. Low-velocity impact (LVI) testing serves as a means to quantify the allowable impact energy the structure can withstand, and to assess the typical failure modes encountered during this type of loading. The objectives of this paper are: to study the response of plain AAC and CFRPAAC sandwich struc¬tures to low-velocity impact and to assess the damage perfor¬mance of the panels; to study the effect of CFRP laminates on the impact response of CFRPAAC panels; and to study the effect of the processing method (hand lay-up versus vacuum assisted resin transfer molding) and panels’ stiffness on the impact response of hybrid panels. Impact testing was conducted using an Instron drop-tower testing machine. Experimental results showed a significant influence of CFRP laminates on energy absorption and peak loads of CFRPAAC panels. A theoretical analysis was conducted to predict the energy absorbed by CFRPAAC sandwich panels using the energy balance model. Results found were in good accordance with the experimental data.