International Concrete Abstracts Portal

Today, in Russia, carbide - silicon and aluminate - silicate packing masses are generally used for lining blast - furnace chutes. They contain re-fractory clay, coal-tar pitch and resins as binders which emit carcinogenic sub-stance dangerous for a human organism. Thirty compositions of chute concrete masses excluding any carcinogenic substance were studied and tested on a chute by the Siberian State University of Industry in conjunction with the Kuznetsk Metallurgical Combine company. The best results were obtained with the following composition: 75 % fused electrocorundum, 20 % refractory clay, 5 % high-alumina cement and 7.3 % water (above 100 %). Thermal resistance in heat changes was above 25 cycles at 800 ‘C, apparent density was 2.54 to 2.75 g/cm3, compressive strength was 76.6 and 79.2 MPa at 110 ‘C and 1450 ‘C, respectively, slag resistance was 0.1 to 0.2 mm at 1450 ‘C, firing shrinkage was 0.2 % with no corrosion observed. The composition developed increased the service life by 10 times compared with the composition generally applied and does not emit any carcinogenic matters. However, in view of the economic crisis and high cost of the electrocorundum, its application is limited. Therefore, we have developed compositions with a high - alumina product (HAP), the waste from the Yurga abrasive works, as a replacement for the electrocorundum. They are as follows: (i) 35 % HAP, 20 % fireclay powder, 15% refractory clay, 30 % waste from the production of silicon carbide; (ii) 48 % HAP, 20 % fireclay powder, 15 % refractory clay, 32 % waste of silicon car-bide with a particle size distribution of 3 to 0 mm. These compositions exhibit < 50 % reduction in strengths (from 80 to 40 MPa) at 1450 ‘C with other indices (slag resistance, iron resistance, apparent density and shrinkage) being the same as for compositions containing pure fused electrocorundum. Their cost is simi-lar to that of the concrete masses generally used but the service life is 4 times longer which was proved by testing in a central chute of a blast furnace.

Concrete structures in aggressive environments are prone to a reduction in their design service-life due to one or more of the following causes: reinforcement corrosion, sulfate attack, chemical attack etc. In addition to utilizing a good quality concrete, protective measures, such as use of coated bars, and/or application of surface coatings, are now commonly utilized by the construction industry worldwide. Cement-based coatings are now widely used as they are considered to be safe from the point of view of preserving the alkaline nature of concrete pore solution. This paper presents results of an investigation conducted to evaluate the performance of cement-based surface coatings in environments commonly occurring in the field. The performance of selected cement-based surface coatings was evaluated by ascertaining their adhesion to the concrete substrate, crack bridging ability, chloride diffusion, moisture resistance, water permeability, carbonation diffusion, and chemical resistance. Best adhesion was exhibited by the epoxy-modified cementitious coating. Similarly, the chloride permeability was also the lowest in this type of coating. The crack bridging ability of the polymer modified cementitious coating was better than other cement-based coatings investigated in this study. These results indicate that epoxy modified cement-based coating provides adequate protection to concrete.

The moisture condition of the substrate surface prior to repair influences the plastic shrinkage and resultant physical properties of the repair material after repair. Absorption of moisture by the substrate may cause not only plastic shrinkage of the repair material adjacent to the interface, but also expansion at the surface to be repaired due to uptake of moisture and may lead to the premature debonding of the repair material. In this investigation, substrate prisms of four different thicknesses (30, 48, 66 and 1OOmm) under three different moisture condition (oven dry, natural dry and saturated surface dry) were employed to investigate the absorption and expansion of the substrate when it is immersed in water or comes into contact with the freshly cast repair material. Based on the test results obtained, a suitable pre-wetting time before repair work is begun is proposed.

Ferrocement, a thin structural composite material, exhibits better crack resistance, higher tensile strength-to-weight ratio, ductility and impact resistance than conventional reinforced concrete. These properties have been exploited through the use of ferrocement for structural upgrading and the rehabilitation of concrete structures. This paper highlights over 20 years of research and innovative applications of ferrocement by a team of researchers at the Centre of Construction Materials and Technology at the National University of Singapore. A number of successful commercial precast applications of ferrocement for use in the upgrading of building fixtures and services have resulted from the research carried out. Salient features of the design, construction and performance of ferrocement structural elements used in upgrading and rehabilitation are discussed briefly in this paper. Experimental studies into the durability, strength and impact properties are also discussed. Once viewed as a labour intensive construction material, the production of ferrocement precast elements through mechanization have rendered the material competitive and economically viable for use in construction, upgrading and structural rehabilitation in land scarce Singapore with its high labour cost.

Protective coatings are often used to waterproof their substrate, to increase the durability of concrete, or simply to improve the aesthetics of a structure. However, there are side effects. For example, coatings that shed water would inhibit the curing effect that could be derived from subsequent wetting due to outdoor exposure. A protective coating could also increase the carbonation of its substrate since it provides a favourable dry environment for carbonation to proceed. This paper presents long-term results to illustrate these two ‘side effects’ on the use of protective coatings.