Search Results (2)

There have been numerous studies on shotcrete based on strength and durability. However, few studies have been conducted on rheological characteristics, which are very important parameters for evaluating the pumpability and shootability of shotcrete. In those studies, silica fume has been generally used as a mineral admixture to simultaneously enhance the strength, durability, pumpability, and shootability of shotcrete. Silica fume is well-known to significantly increase the viscosity of a mixture and to prevent material sliding at the receiving surface when used in shotcrete mixtures. However, the use of silica fume in shotcrete increases the possibility of plastic shrinkage cracking owing to its very high fineness, and further, silica fume increases the cost of manufacturing the shotcrete mixture because of its cost and handling. Colloidal silica is a new material in which nano-silica is dispersed in water, and it could solve the above-mentioned problems. The purpose of this research is to develop high-performance shotcrete with appropriate levels of strength and workability as well as use colloidal silica for normal structures without a tunnel structure. Thereafter, the workability of shotcrete with colloidal silica (2, 3, and 4%) was evaluated with a particle size of 10 nm and silica fume replacement (4 and 7%) of cement. In this study, an air-entraining agent for producing high-performance shotcrete was also used. The rheological properties of fresh shotcrete mixtures were estimated using an ICAR rheometer and the measured rheological parameters such as flow resistance and torque viscosity were correlated with the workability and shootability. More appropriate results will be focusing on the Bingham model properties such that the main focus here is to compare all data using the Bingham model and its performance. The pumpability, shootability, and build-up thickness characteristics were also evaluated for the performance of the shotcrete. This research mainly focuses on the Bingham model for absolute value because it creates an exact linear line in a graphical analysis, which provides more appropriate results for measuring the shotcrete performance rather than ICAR rheometer relative data. Full article

In the rapidly developing modern society, many raw materials, such as crushed limestone and river sand, which are limited, are consumed by the concrete industry. Naturally, the usage of waste materials in concrete have become an interesting research area in recent years, which is used to reduce the negative influence of concrete on the environment. Hence, this paper presents the development of a sustainable lightweight wet-mix shotcrete by replacing natural coarse gravel with a kind of byproduct, nut shell (walnut). Fibers made from dumped polyethylene terephthalate (PET) bottles were mixed in the composite to improve the properties of the lightweight wet-mix shotcrete. The initial evaluation of the fresh concrete mixed with different volume fraction of walnut shell was carried out in terms of its performance capacities of mechanical properties (i.e., tensile and compressive strength), pumpability and shootability (i.e., slump, pressure drop per meter and rebound rate) and the results were compared with plain concrete. With increase of walnut shell, compressive and splitting tensile strength of casting concrete decreased, while slump and pressure drop reduced slightly. Additionally, appropriate dosage of walnut shell can improve the shootability of fresh concrete with low rebound rate and larger build-up thickness. In the second series tests, polypropylene (PP) fiber and multi-dimension fiber were also mixed in composite for comparative analysis. After mixing fibers, the splitting tensile strength had obtained marked improvement with slight reduction of compressive strength, along with acceptable fluctuation in terms of pumpability and shootability. Furthermore, relation of density and compressive strength, relation of rebound and density, build-up thickness and relation of compressive and splitting tensile strength were discussed. This study found wet-mix shotcrete incorporating PET fiber with walnut shell of about 35% coarse aggregate replacement could be used for roadway support as lightweight shotcrete per requirements of mine support. Full article