International Concrete Abstracts Portal

ACI 318, “Structural Concrete Building Code,” has been completely reorganized for the 2014 edition. While the technical provisions of most of the code have been unchanged, changes have been made in the provisions dealing with responsibility, durability, and construction. The responsibility for use of the code has been assigned to the licensed design professional (LDP.) Minor changes have been made to the durability provisions to clarify the intent of the code and to help the LDP select exposure classes. The most significant changes in ACI 318-2014 are in a new chapter that addresses construction requirements. Previously, construction provisions were located throughout the code. The new code is based upon the premise that the contractor should not have to search the code for construction requirements. Instead, all such requirements must be in the construction documents that are a part of the contract between the owner and the contractor. The new chapter makes the LDP responsible for writing the applicable design information and compliance requirements into the construction documents.

Materials for grouting post-tensioning tendons of a bridge at below freezing temperature (–10oC or 14oF) were studied. The water/cementitious material ratio was a maximum of 0.32 and the grout properties were tested at -10oC (14oF) according to applicable Chinese standards for past-tensioning grouts. After special treatment, the efflux times of the modified grouts were between 14 and 22 seconds after mixing and less than 30 seconds after 60 minutes without agitation. The final strength of the grout reached 50-60 MPa (7975-8700 psi) after 35 days of curing (7 days at below freezing temperature and 28 days at a standard temperature), which was 95%-100% of the reference strength for curing at a standard temperature.

Fiber-reinforced polymer (FRP) reinforcement for concrete has gained popularity in the past two decades due to its high strength, cyclic load resistance, and insensitivity to chloride corrosion. This paper presents the results of an experimental evaluation of FRP reinforcing bars made completely from recycled materials with two surface conditions: externally bonded helical glass rovings and lathed circumferential grooves. Tensile testing indicated that only grooved bars provided adequate bonding within concrete systems due to bond failure of the external helical rovings under tensile loading. The performance of 1.0 m (39.4 in.) hollow beams reinforced with grooved recycled bars, commercially available FRP bars, and #2 (6.4 mm or 0.25 in.) steel bars was evaluated. Recycled and commercial FRP-reinforced beams had nearly identical performance, indicating that the recycled bars are feasible for use as reinforcement in concrete, although neither FRP-reinforced beam performed as well as steel-reinforced beams.

In the present study, the effects of porous ceramic waste aggregate (PCWA) on the mechanical properties and durability of the steam-cured fly ash concrete are investigated. The replacement ratios of fly ash were 0%, 20% and 40% by mass, and those of PCWA were 0%, 10% and 20% by volume. Three kinds of curing conditions: dried after steam curing (D-Steam), sealed after steam curing (S-Steam), and sealed curing (Sealed), were used. The experimental results show that the compressive strength of the fly ash concrete with 20% replacement of PCWA increased regardless of curing conditions, and the pore volume decreased. The autogenous shrinkage of the S-Steam cured fly ash concrete was reduced significantly by using 20% replacement of PCWA. The carbonation resistance of the D-Steam cured fly ash concrete was also improved by using 10% replacement of PCWA and 40% replacement of fly ash.

Durability based design of RC structures has gained great significance in recent decades and various mathematical models have been proposed. One of the famous models was proposed by fib. The effect of local conditions on the prediction of the models is one of the most important issues. Hence, regional investigations are necessary. The Persian Gulf is one of the most aggressive regions of the world. In this study, the fib model performance was evaluated by comparison with field measurements on some marine RC structures located in this region. The results show that the parameters in the fib model did not result in good agreement with some of field data. The model parameters were modified for application to this environment. In order to do this, a laboratory study was performed and nine different concrete mixtures with various percentages of silica fume were prepared. Evaluation of the modified model results shows that the modifications produced more reliable results than the original model for this environment.