Studies on Lightweight High-Strength Shotcrete
With small deadweight, light-weight shotcrete can avoid the shotcrete lining from falling off, which benefits the bolt-shotcrete support of the roadway better under same bond strength. Light-weight shotcrete can be made by using clay ceramsite, polystyrene particles and fly-ash ceramsite to replace some gravel and sand. The experiments show that the characteristic of fly-ash ceramsite shotcrete is superior to that of clay shotcrete, while by replacing part of gravel and sand with polystyrene particles and fly-ash ceramsite, light-weight high strength shotcrete will have excellent combination properties.
Grey target decision analysis of optimum mixing ratio of LWAS based on the comprehensive performance
Abstract Aiming at the problems of complicated data processing, large amount of calculation, perplexing results of the orthogonal test, and the uncertain multi-index decision-making matter that the decision-making index value is difficult to be refined, this paper studies the mixed multi-index gray target decision-making model with three data types of real value, interval number and triangular fuzzy number. According to the basic connotation of decision gray target and uncertain decision information, a hybrid ellipsoid gray target is defined, and a mixed gray target decision model is established. Then through the mechanical, durability, workability and other performance, the lightweight aggregate shotcrete (LWAS) was selected for the optimization of the mix ratio, and then compared with the traditional orthogonal results, and applied in the tunnel engineering. Therefore, the feasibility of applying LWAS in tunnel bolting and shotcreting supporting was explored to provide a theoretical reference for the application of LWAS in tunnel lining. The results show that: (1). The unit water consumption has some influences on the compressive strength, Splitting tensile strength, bonding strength and resistance to chloride ion permeability of the LWAS, and the optimal range of water consumption is 180–200 kg/m3. (2). The water-binder ratio has a significant effect on the compressive strength, splitting tensile strength and electric flux of LWAS, and has a small effect on the bonding strength. (3). The compressive strength, splitting tensile strength and electric flux of concrete increase with the decrease of water-binder ratio. (4). When the fly ash content is 0%, the 28 d compressive strength, splitting tensile strength and bonding strength of LWAS are the largest, and the electric flux is the smallest. (5). When the water-cement ratio is 0.42 with pure cement, the combination of gray targets has the best comprehensive decision-making performance, and it is recommended as the tunnel lining concrete ratio.
CHLOIRIDES AND CORROSION IN THE ARABIAN GULF ENVIRONMENT
In order to aid in designing future reinforced concrete buildings, different codes and publications and the results of inspections of more than 60 buildings in the Arabian Gulf were reviewed in an effort to ascertain a corrosion threshold value that is valid for the particular conditions present there. Recommended limits are discussed, as well as experience in Abu Dhabi, and the implications for design of the observations made. The study concluded that the chloride limits now in use are not stringent enough, and that more stringent limits and good supervision to ensure compliance are needed.