International Concrete Abstracts Portal

A natural amorphous silica with a purity of approximately 90% is mined from an extensive geothermal deposit near Rotorua, New Zealand. After refining and processing to remove impurities, the ‘Microsilica 600TM’ has properties which comply with Australian Standard AS 3582 Part 3 ‘Silica Fume’ as a supplementary cementitious material for use with portland cement. The performance characteristics of concrete incorporating the ‘Microsilica 600’ were evaluated at two cement levels of 320 and 400 kg/m 3 and two silica addition levels of 7 and 10%. Properties evaluated were compressive strength, tensile strength, concrete shrinkage, sulfate resistance, resistance against chemical attack, abrasion resistance, and chloride permeability. Performance improvement compared favorably with published data on concretes incorporating processed ‘conventional’ silica fume.

Rice husk ash (RHA) is a very reactive pozzolanic material. It has been succesfully used as a mineral admixture in concrete. Rice husks are readily and in large quantities available in Vietnam. Hence, it would be of economic interest to study the use of RHA for the production of high-strength and durable concretes based on indigenous raw materials. This con-cept should also encompass the aggregates, with coarse-grained crushed rock (granite) and very fine river sand as natural candidates. The particle size distribution of this sand violates the building code, however. Since blending with coarse (imported) sand would be too expensive, this study focused on gap-graded mixtures. For the binder an ASTM Type I portland cement was employed, being the only quality produced in the region in Vietnam. RHA with a significant carbon content was obtained after burning rice husks at temperatures below 75OOC. The ash was thereupon finely ground in conjunc-tion with a naphtalene-based superplasticizer. The application of the RHA in conjunction with this superplasticizer in the gap-graded concretes with very fine sand made it possible to produce high consistency and cohesive mixtures with a relatively low sand content. 28-days compressive strengths values of 70-90 MPa were obtained for mixtures with slumps of 140-225 mm and water to binder ratios of 0.40-0.33. For stiff mixtures, with water to binder ratios of 0.35-0.27, the 28-days compressive strength values were in the range of 60-100 MPa.

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.

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.

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.