Strength and Durability Properties of Antimony Tailing Coarse Aggregate (ATCA) Concrete

Antimony (Sb) is a trace element applied widely in modern industry. A large number of tailing solid wastes are left and accumulated in the mining area after purifying the precious antimony from the antimony ores, causing serious pollution to the environment. The major aim of this study is to investigate the feasibility of utilizing antimony tailing coarse aggregate (ATCA) as a complete substitute for natural coarse aggregate (NCA) in high-strength concrete. Concrete specimens with 25%, 50%, 75%, and 100% ATCA replacing the NCA in conventional concrete were prepared for evaluating the performance of ATCA concrete. The investigators find that ATCA concrete has good workability, and the mechanical properties and long-term behavior (shrinkage and creep) of ATCA concrete with all replacement levels are superior to those of NCA concrete. The durability indices of ATCA concrete, such as the frost-resistant, chloride permeability, and resistance to carbonation, are better than those of NCA concrete. While the alkali activity and cracking sensitivity behavior of ATCA concrete seem to be decreased, nevertheless, the difference is not significant and can be neglected. The researchers demonstrate that all of the control indices of ATCA concrete meet the requirements of the current industry standards of China. Overall, ATCA can be used in concrete to minimize environmental problems and natural resources depletion.

Experimental Evaluation of Shrinkage, Creep and Prestress Losses in Lightweight Aggregate Concrete with Sintered Fly Ash

The paper presents the experimental results of shrinkage, creep, and prestress loss in concrete with lightweight aggregate obtained by sintering of fly ash. Two concrete mixtures with different proportions of components were tested. Concrete with a density of 1810 and 1820 kg/m3, and a 28-day strength of 56.9 and 58.4 MPa was obtained. Shrinkage and creep were tested on 150 × 250 × 1000 mm3 beams. Creep was tested under prestressing load for 539 days and concrete shrinkage for 900 days. The measurement results were compared with the calculations carried out according to the Eurocode 2 as well as with the results of other research. A very low creep coefficient and lower shrinkage in relation to the calculation results and the results of other research were found. It was also revealed that there is a clear correlation between shrinkage and creep, and the amount of water in the concrete. The value of the creep coefficient during the load holding period was 0.610 and 0.537, which is 56.0 and 49.3% of the value determined from the standard. The prestressing losses in the analyzed period amounted to an average of 13.0%. Based on the obtained test results, it was found that the tested lightweight aggregate concrete is well suited for prestressed concrete structures. Shrinkage was not greater than that calculated for normal weight concrete of a similar strength class, which will not result in increased loss of prestress. Low creep guarantees low deflection increments over time.

Experimental Investigation of MgAl-NO2 and MgAl-CO3 LDHs on Durability of Mortar and Concrete

Two kinds of layered double hydroxides (LDHs), MgAl-NO2 (N-LDH) and MgAl-CO3 (C-LDH), were incorporated to study the durability of mortar and concrete. The LDH contents of mortar were 1%, 2%, and 4% by mass and the LDH contents of concrete were 0.5%, 1%, 2%, 4%, respectively. The effect of LDHs on sulfate resistance of mortar was studied through dry-wetting cycle test, compressive strength test, and flexural strength test. In addition, the effects of LDHs on pore structure, chloride resistance, carbonation resistance, shrinkage, and creep of concrete were investigated by SEM, mercury injection test, XRD, chloride ion diffusion coefficient test, chloride salt corrosion depth test, carbonation depth test, shrinkage test, and creep test. The results showed that LDHs can improve the ability of resisting ion corrosion, carbonization, shrinkage, and creep, reduce the pore content, and optimize the pore structure of mortar and concrete to some extent. Moreover, 4% LDHs had a better effect on improving the durability of mortar and concrete compared to 0.5%, 1%, and 2% LDHs, and the effect of C-LDH was better than N-LDH.

Studying the Relationship between the Strength and Stress-Related Characteristics of Concrete as a Conglomerate and the Properties of its Components

The concrete conglomerate properties change over time and depend on a number of factors. When considering deformation under the effect of mechanical loads or changes in temperature and humidity, the mechanism of this process is based on three main provisions. Firstly, concrete is a composite material, the matrix of which is cement stone. Secondly, the elastic modulus and strength of the cement stone may be less or more than that of aggregate. Thirdly, the concrete destruction under axial compression occurs at the cement stone stresses exceeding its ultimate extensibility in the direction normal to the external load action. Considering the specifics of deformation under load in different periods and the role of stress-related characteristics in this process, it is advisable to outline ways to regulate them and thereby the main concrete properties in the desired direction. The importance and feasibility of this approach are determined by the need to develop techniques allowing control of properties such as elasticity, shrinkage, and creep. A series of experimental tests and a comparative analysis of the results have been performed. The effect of some aggregate rocks on certain strength and stress-related properties of the concrete conglomerate has been investigated. Limestone and sandstone have been taken as the rocks studied. The properties studied include impact, axial compression, and axial tensile strengths. According to the analysis, concrete prepared on crushed limestone has shown the best results concerning all the properties studied.

Investigation of measured prestress losses compared with design prestress losses in AASHTO Types II, III, IV, and VI bridge girders

Inaccurate prediction of prestress losses leads to inaccurate predictions for camber, deflection, and concrete stresses in a bridge girder. This study aims to improve the prediction of prestress losses and provides bridge designers with insights into the differences between design and actual concrete properties. Prestress losses, compressive strength, modulus of elasticity, shrinkage, and creep were measured for several American Association of State Highway and Transportation Officials (AASHTO) Types II, III, IV, and VI girders. The investigation revealed that the measured total prestress losses at the time of deck placement were lower than the design losses calculated using the refined estimates method of the 2017 AASHTO LRFD Bridge Design Specifications. This was mainly attributed to the actual concrete compressive strength at transfer being greater than the design compressive strength. This discrepancy was as high as 73% for some girders. It was also determined that the 2017 AASHTO LRFD specifications’ refined estimates method for estimating prestress losses overestimates the total prestress losses at the time of deck placement for AASHTO Types II and III girders.