International Concrete Abstracts Portal

The potential of using the stainless steel coatings to protect steel reinforcing bars from corrosion especially in a salt contaminated concrete environment was evaluated. Type 304, 3 16 and 420 stainless steel coated coupons and reinforcing bars were prepared using the Twin-Wire Electric Arc (TWEA) and High Pressure/High Velocity Oxygen-Fuel (HP/HVOF) processes. Metallographic examinations were conducted to determine the coating density and the oxide content. The corrosion resistance of the coatings was evaluated using linear polarization and salt spray techniques. The stainless steel coating prepared using the HP/HVOF process had a much superior corrosion resistance performance than those prepared using the TWEA process. The former process produced a dense, low oxide content coating while the latter produced relatively porous coatings.The oxide content of the coating in the TWEA process can be significantly reduced using argon or nitrogen as primary and arc jet gases. This did not have a significant effect on porosity of the coating.

This paper describes the results of an ongoing test program to evaluate the performance of polymer-modified cement-based mortars for repairing surfaces up to a depth of 75 mm (3 inches) of concrete structures damaged due to exposure to cold climates. Twenty-five selected commercially available polymer-modified products, seven containing styrene butadiene rubber (SBR) and 18 containing acrylics were evaluated. They were compared with a pure cement-based mortar containing 8% silica fume with a water/(cement + silica fume) (W/C) ratio of 0.3 1. All of the mortars were subjected to physical and mechanical tests such as thermal compatibility with base concrete, drying shrinkage, permeability, abrasion-erosion resistance, bond strength, compresive strength and freezing and thawing. The thermal compatibility with the base concrete test at temperatures from -50°C to +5O°C was used as a preselection test. The test data indicated that the polymer-modified mortars, even from the same family, i.e. SBR or acrylics, showed mixed results, with their performance varying from one manufacturer’s product to another. This paper also presents the performance of the three best polymer-modified cement-based mortars (included in the 25 mortars), installed in 1992 on two spillways of a dam in a very severe environment. These mortars were exposed to the abrasive action of water-borne sediments as well as the stresses related to hydraulic pressure and rigorous freezing and thawing and drying/wetting cycles. The six inspections so far have found that these three products are still performing well after an exposure to very low temperatures for a period of four years.

Jetty structures were constructed at Kobe Port as part of the reconstruction project after Hanshin Great Earthquake in 1995. In this jetty structure, straight and oblique base piles were jointed with a precast slab in the field to shorten the work period. This paper presents the results of experiments carried out in a laboratory, the full scale filling test using a super workable concrete applied to the joints of structure, and the concrete quality. Super workable concrete containing a viscosity agent, gypsum, and ground granulated blast-furnace slag was used to satisfy the requirements for its high filling ability, minimized bleeding, and reduced shrinkage. Super workable concrete was produced and placed from a concrete plant ship in this construction.

The effectiveness of calcium hitrate (CN) as a setting accelerator for cement is dependent on the cement type. The reason for this is explained by the mechanisms for set acceleration, and parametres for predicting the set accelerating efficiency of CN from cement characteristics is pointed out. Performance characteristics such as temperature evolution profile in insulated concrete (i.e. semi-adiabatic) and early compressive strengths (from 8 h) of concretes cured at 20°C for different additiom of different soluble calcium salts are demonstrated. The accelerating effect of CN was compared to additions of both calcium acetate and fortnate on equimolar concentrations of Ca2+ Calcium acetate and formate gave about the same accelerating effect, while CN showed greater acceleration. The difference might be due to an increased content of free Ca2+ (i.e. hot complexed ion) in CN compared with the organic acid salts. The temperature profiles revealed that CN accelerates set and hot the rate of early strength development. However, the 8 h compressive strength was increased when CN was added due to parallel displacement of the temperature evolution curves towards earlier times. Examples are given for field use (e.g. regulating slip forming rates) and potential applications (e.g. element production) of CN in concrete.

The department of civil enginering of the Siberian State Academy for Mining and Metallurgy (SSAMM) together with Tom-Usinsk Precast Works have developed compositions and technology for producing a lightweight concrete based on ash and slag from Tom-Usinsk power plant. The concrete can be used for external wall panels as a replacement for daydite concrete. The ash slag blend from hydrodumps of the power plant contains 33% ash, 52% slag sand with a particle size of 0.14 to 5 mm and 15% slag with a particle size of 5 to 10 mm. The blend meets the requirements of Russia Standard 25592-91 for use in concretes as an aggregate. Compressive strength of the concrete ranged from 5 to 10 MPa depending on the degree of air-entrainment and the function of panels. Average density of the concrete mixture was in the range of 1070 to 1150 kg/m3 before placing and 1100 to 1200 kg/m3 after placing, compacting and heat treatment, the coefficient of heat conductivity of the light-weight concrete was in the range of 180 to 250 W/m oC depending on average density and strength. The thickness of wall panels produced from this concrete could be reduced to 400 mm with out any warm coating. The concrete developed has-been patented and tested at the Tom-Usinsk reinforced concrete works. The cost of 1 m3 of external wall panels produced from the concrete is 30% lower than that of panels made from claydite concrete.