International Journal of Concrete Structures and Materials

Recycling scrap tires provides an alternative source of fine aggregates for the production of rubberized concrete and this will lead to significant increase in concrete frost resistance, environmental protection, and conservation of natural sand and gravel resources. In this paper, a total of 25 groups of rubberized concrete were produced by adding scrap tire rubber particles of different sizes, contents, and pretreatment methods to replace the fine aggregate, and their compressive strength during freeze–thaw cycles was studied from both the macro- and meso-perspectives. The results indicated that the decrease in concrete strength and weight was notably restricted by the presence of rubber particles during freeze–thaw cycles. The rubber fine aggregate with smaller particle sizes enhanced the concrete frost resistance more significantly, and the F100 of concrete with rubber particles of 1.0–2.0 mm increased from 76.6 to 86.5% by increasing the rubber content from 0.0 to 5.6%. The effects of rubber fine aggregate on concrete compressive strength during freeze–thaw cycles were quantified. On this basis, a forecast model for rubberized concrete compressive strength in freeze–thaw cycles was proposed, and the effects of the particle size, content, and pretreatment of the rubber particles were considered. The calculated results agreed well with the test results both in this study and the relevant peer studies, indicating that the model can provide a good reference for the design and engineering application of rubberized concrete in frigid environments.

To study the hybrid effects of polypropylene fiber and basalt fiber on the fracture toughness of concrete, 13 groups of notched concrete beam specimens with different fiber contents and mass ratios were prepared for the three-point bending test. Based on acoustic emission monitoring data, the initiation cracking load and instability load of each group of specimens were obtained, and the fracture toughness parameters were calculated according to the double-K fracture criterion. The test results show that the basalt fiber-reinforced concrete has a greater increase in initial fracture toughness, and the toughness of coarse polypropylene fiber-reinforced concrete is more unstable. Moreover, after the coarse polypropylene fiber content reaches 6 kg/m3 and the basalt fiber content reaches 3 kg/m3, increasing the content will not significantly improve the fracture toughness of the concrete. The polypropylene–basalt fiber will produce positive and negative effects when mixed, and the mass ratio of 2:1 was optimal. Finally, the fitting analysis revealed that the fracture process of polypropylene–basalt fiber-reinforced concrete (PBFRC) can be objectively described by the bilinear softening constitutive curve improved by Xu and Reinhardt.

The objective of this work was to examine the influence of carbonation on the microstructure of cement materials. Different materials, which were CEM I mortar and paste, CEM II mortar and paste, were carbonated at 20 °C, 65 % relative humidity and 20 % of CO2 concentration. The specific surface area and pore size distribution were determined from two methods: nitrogen adsorption and water adsorption. The results showed that: (1) nitrogen adsorption and water adsorption do not cover the same porous domains and thus, we observed conflicts in the results obtained by these two techniques; (2) the CEM II based materials seemed to be more sensible to a creation of mesoporosity after carbonation than the CEM I based materials. The results of this study also helped to explain why observations in the literature diverge greatly on the influence of carbonation on specific surface area.

Large scale constructions needs to estimate a possibility for pumping concrete. In this paper, the state of the art on prediction of concrete pumping including analytical and experimental works is presented. The existing methods to measure the rheological properties of slip layer (or called lubricating layer) are first introduced. Second, based on the rheological properties of slip layer and parent concrete, models to predict concrete pumping (flow rate, pumping pressure, and pumpable distance) are explained. Third, influencing factors on concrete pumping are discussed with the test results of various concrete mixes. Finally, future need for research on concrete pumping is suggested.

This paper presents results of an experimental study which investigates the effect of industrial pozzolan made from calcined silt of dam at 750 °C for 5 h, on mechanical properties and durability of ordinary mortar, compared to the silica fume. Mortar specimens prepared with 5, 10 and 15 % of calcined silt to substitute cement were evaluated for their compressive and flexural strength, sulfate, acid and penetration of chloride ions resistance. The results were compared with ordinary mortar (without addition) and mortar containing 10 % of silica fume. The results obtained showed that the calcined silt of dam has a high potential to be used as a pozzolanic material, it improves the strength and the durability of mortar and compete the silica fume.

Apart from its recognized strengthening effect for shear loading, the presence of stirrups in reinforced concrete results in an increase of the ductility of structural members and in the capacity of reaching higher longitudinal compressive stress levels provided by transversal confinement. These effects are usually represented phenomenologically in fibre beam models by artificially increasing the compressive strength and the ultimate compressive strain of concrete. Two numerical formulations for layered beam descriptions accounting explicitly for transversal confinement are implemented and assessed in this contribution. The influence of stirrups is incorporated by means of a multi-dimensional yield surface for concrete, combined with equilibrium constraints for the transversal direction involving concrete and steel stirrups, and with a concrete ultimate strain dependent on the hydrostatic stress. This contribution focuses on the numerical formulations of both frameworks, and on their assessment against experimental results available in the literature.