This study evaluates the potential to use shrinkage-reducing admixture (SRA) and pre-saturated lightweight sand (LWS) to shorten the external moist curing requirement of ultra-high-performance concrete (UHPC), which is critical in some applications where continuous moist curing is challenging. Key characteristics of UHPC prepared with and without SRA and LWS and under 3 days, 7 days, and continuous moist curing were investigated. Results indicate that the combined incorporation of 1% SRA and 17% LWS can shorten the required moist curing duration since such mixture under 3 days of moist curing exhibited low total shrinkage of 360 µε at 56 days and compressive strength of 135 MPa (19,580 psi) at 56 days and flexural strength of 18 MPa (2,610 psi) at 28 days. This mixture subjected to 3 days of moist curing also had a similar hydration degree and 25% lower capillary porosity in paste compared to the Reference UHPC prepared without any SRA and LWS and under continuous moist curing. The incorporation of 17% LWS promoted cement hydration and silica fume pozzolanic reaction to a degree similar to extending the moist curing duration from 3 to 28 days and offsetting the impact of SRA on reducing cement hydration. The lower capillary porosity in the paste compensated for the porosity induced by porous LWS to secure an acceptable level of total porosity of UHPC.

The objective of the present study is to assess the flexural residual strengths of lightweight aggregate concrete (LWAC) reinforced with micro-steel fibers. Further, the material class of such concrete was examined through comparison with the fiber-reinforced concrete classification specified in the provisions of fib 2010. Fourteen beam specimens were classified into L (21 MPa [3.05 ksi]) and H (40 MPa [5.80 ksi]) groups according to the design compressive strength of LWAC. The volume fraction of micro-steel fibers varied from 0 to 1.5% at a spacing of 0.25% in each beam group. From the beam test results under the three-point loading condition, flexural stress-crack mouth opening displacement (CMOD) curves were measured and then discussed as a function of the fiber reinforcing index (βf). The flexural residual strengths corresponding to four different CMOD values (0.5, 1.5, 2.5, and 3.5 mm [0.02, 0.06, 0.1, and 0.14 in.]) were compared with previous empirical equations and fib 2010 classification. The various analyses of the measured results indicate that βf can be regarded as a critical factor in directly determining the magnitude of flexural residual strengths and assessing material classification. The proposed refined equations improve the accuracy in predicting the flexural residual strengths of concrete beams with different densities and reinforced with different types of steel fibers. Consequently, microsteel fibers are a promising partial replacement for conventional steel reinforcing bars to enhance the ductility of LWAC elements.

The purpose of this study is to investigate the effect of steel fiber content and type on the compressive and flexural ductility capacities of lightweight aggregate concrete (LWAC). Fiber-reinforced LWAC specimens were divided into four groups according to the type of fibers, such as conventional macrosteel fibers (SFs) with hooked ends, straight copper-coated microsteel fibers (CMSFs), crimping-shaped CMSFs, and hooked-end CMSFs. The fibervolume fractions (Vf) were 0.5, 1.0, and 1.5%. This study also modifies the ASTM C1018 method by using the initial crack point calculated from the elastic theorem to save a tedious and elaborated effort in determining the reference point at the load-deflection curve, particularly for beams with a strong hardening response. The test results revealed that the hooked-end CMSFs were better than SFs and crimping-shaped CMSFs with the same shape and length at decreasing the slope of the applied loads at descending branches of the compressive stress-strain and flexural load deflection curves for the LWAC. Compressive and flexural toughness indexes were derived as functions of the fiber reinforcing index based on the regression analysis of test data to assess the ductility improvement of LWAC with steel fibers.

The aim of this study was to determine the effect of different amounts of filler on concrete properties. An experimental approach has made it possible to develop a construction product made from limestone dust, which is considered waste. This paper presents an experimental study on the prospects of using a mixture of waste limestone powder for the manufacture of an economical and lightweight composite as a building material. This paper also presents the results of research on the possibility of using limestone dust as an aggregate in the production of concrete with lightweight aggregates. In this way, different amounts of limestone dust were used. Tests were conducted on concrete to replace 30, 50, and 70% by weight of coarse aggregate. The mechanical properties of concrete mixtures with high proportions of limestone dust were examined. The achieved compressive strength, flexural strength, and unit weight correspond to current international standards.

The current study examines the effect of steel fiber content on the uniaxial compressive response of lightweight concrete to propose a stress-strain model in cyclic loading. For this purpose, 150 x 300 mm cylindrical specimens containing different volume ratios of steel fiber (0, 0.5, 1, and 1.5%) were tested to plot the cyclic curves of steel fiber-reinforced lightweight aggregate concrete (SFRLWAC). The best combination of two types of steel fibers was used in this research: straight hooked-end and crimped fibers with aspect ratios of 50 and 28.5, respectively. Key points on cyclic curves were examined, and the compressive behavior of lightweight concrete was investigated. The results show that the integration of steel fibers reduces the plastic strain and stiffness degradation of the reloading paths. Furthermore, a rise in steel fiber volume fraction is associated with increased common-point coordinates. A stress-strain relationship was proposed to define the compressive cyclic behavior of SFRLWAC. The model was compared with the experimental findings to confirm its validity. The proposed model shows satisfactory agreement with the experimental results.