International Concrete Abstracts Portal

This paper presents the concrete structure repairing method, using concrete with expanded polystyrene granules (EPS). Reinforced concrete slabs are cast with depression of the top surface up to 70 mm. For the top surface leveling, with minimum selfweight load addition, a new flooring system is developed: over the sound isolation layer, EPS concrete leveling layer, 60-130 mm thick, (p = 450-500 kg/m3, Bk = 1-2 MPa) is cast. As a top finishing surface, high performance concrete layer, 15 mm thick (Pk = 60 MPa) is cast. Flooring system satisfied all the requirements, with total weight of 55-90 kg/m2.

The cracking behaviour of concrete beams having longitudinal tension reinforcement and various combinations of volume and aspect ratio of hooked end steel fibers was investigated experimentally. Eight full-scale beams have been tested. The section dimensions (200 x 350 mm2), span length (3250 mm), concrete compressive strength and longitudinal tension reinforcement were kept constant for all beams. The beams were tested at a cube compressive strength of about 40 MPa. The mechanical properties of the steel fiber reinforced concrete under tension were determined according to the Belgian standard NBN B15-238. The addition of steel fibers decreases both the crack spacing and the crack width. A greater reduction of the crack width, crack spacing respectively, can be noticed if steel fibers with a higher aspect ratio are used. Besides the experimental program also a theoretical study has been executed : a modification of the RILEM TC162-TDF-model to predict crack width is proposed.

Experimental studies are reported on upgrading the load carrying capacity of reinforced columns by jacketing with carbon fiber reinforced plastic (CFRP) flexible wraps. Several square columns with medium high strength concrete (cube strength = 64 MPa) were tested under concentric compression. The studied variables include: different upgrading configurations (continuous wrapping all over the height, discontinuous straps, straps concentrated at end zones); volume of wraps; and pre-loading prior to wrapping to simulate in situ strengthening process in practice. Effective wrapping provided lateral confinement to enhance the concrete compressive strength and the load capacity of the columns, in addition to the improvement of the ductility. With higher levels of confinement the axial capacity was further enhanced. Besides, effective retrofitting of preloaded columns restored and even increased their load carrying capacity over that of the original columns. It seems better to use effective full height wraps for enhancement of both strength and ductility and to help restrain against buckling of longitudinal bars, however the effect of confining the columns’ ends cannot be overlooked. The confined concrete strength from tests was compared with those estimated by certain empirical models and the comparisons were favorable in many cases. Other conclusions are also drawn.

The paper discusses the methods used to ascertain the cause of damage to berth No. 4 of the Lae city port in Papua New Guinea and outlines the procedure followed to repair and rehabilitate it. The berth comprising of a concrete deck and supported on steel tube piles was built in 1970. By mid 1990’s, it began showing signs of extensive visible deterioration with widespread corrosion of steel piles and spalling of concrete. To assess the extent of damage, investigation was carried out in two stages with global visual survey in the initial phase and diagnostic testing at selected points in the second stage. The investigation revealed that the mechanism responsible for corrosion was chloride attack. Based on the investigation, remedial measures were recommended for the repair of the berth. The repair and rehabilitation of the berth has been successfully completed and tests done after restoration, estimate the life of the berth to have increased by 15 years.

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.