International Concrete Abstracts Portal

In the present work an acrylic polymer (based on 2-ethylhexyl acrylate) was mixed with cement and fine aggregate and was studied as rubber-like coating to protect reinforced concrete beam specimens. Two acrylic polymer-cement coatings (both with water-cement ratio of 0.50, polymer-cement ratio of 0.50 and fine aggregate-cement ratio of 2) were produced by changing the type of the cementitious component (Portland cement or high alumina cement). The two coatings were applied to a porous concrete substrate with a water-cement ratio of 0.80. Preliminary tests on the uncoated and coated concrete specimens were carried out to study the penetration of water, chloride, sulphate and carbon dioxide. The resistance to penetration of these aggressive agents was very poor in the uncoated specimens and became as good as that of a watertight and durable concrete in the coated specimens. Then coated beam specimens have been kept for 1 year in three different environments (laboratory at 20°C and 65% R.H.; outsides environment exposed to natural changes in temperature and relative humidity; under water) in order to examine the influence of the ageing on the bond strength as well as the flexibility and therefore the ability of the acrylic coatings to bridge the cracks of the concrete substrate. The bond strength of the two coatings was substantially unchanged by the exposure to the three different environments. The flexibility of the polymer-cement coating remained substantially unchanged when portland cement was used independently of the exposure environment. On the other hand, when high-alumina cement was used there was a flexibility loss of the coating in humid environment, particularly in the underwater exposure.

Ferronickel slag is a by-product produced when refining ferronickel from nickel ores. Investigations were conducted for a long time to use this hard slag as aggregate in concrete, and it was standardized in October 1992 as JIS A 5011 (Slag aggregate for concrete). However, one of the types produced in Japan was excluded from the standard, as it was alkali-aggregate reactive. The authors applied various measures specified in other standards to suppress reactivity of this type of ferronickel-slag aggregate, and experimentally confirmed that the following measures are effective: (i) the use of low-alkali cement, (ii) addition of fly ash, and (iii) addition of ground granulated blast-furnace slag.

This paper describes the results of the study on the durability evaluation of Mt. Pinatubo blended cement mortar under accelerated conditions of acidic, sulphate and alkali-silica reactive regimes. Various types of ejecta materials and percentage cement replacements (i.e., 10, 20, 30, 40, 50, 60, 70, and 80%) were investigated to determine the optimum type and proportion in a cement-based mortar matrix based on the criteria of strength, dimension stability, resistance to alkali-aggregate reaction and severe environmental conditions. Test results indicated that the use of Pinatubo pozzolans are effective mineral dmixtures against acidic, sulphate, alkali-aggregate reactions. Optimum pozzolans proportions ranges from 40-60% under varying conditions. Dimension stability and shrinkage properties of mortar with Pinatubo pozzolans are basically comparable to plain portland cement mortar, indicating stability of the pozzolans as a concrete constituent material. Alkali-aggregate reactivity test of selected samples of Pinatubo aggregate also showed innocuous characteristics.

High Performance Concrete (HPC) has been developed primarily for its strength having a compressive strength in excess of 70 MPa, approximately double the strength of conventional concrete. The porosity of this type of concrete, especially when silica fume is added to the mix, much lower than conventional mixes. It is, therefore, assumed that high performance concrete provides significantly better protection against corrosion of reinforcing steel than conventional concrete, but this has not yet been substantiated. A field exposure program is underway with cast-in-place and pre-cast samples, containing embedded reinforcing steel probes exposed to pulp & paper industry effluent at two locations on Vancouver Island, B.C., Canada. The cast-in-place samples were loaded in three-point bending prior to exposure to initiate cracks in the location of the corrosion probes. Probes were also embedded in uncracked areas of the beams. One lower quality concrete, one industrial standard concrete, one HPC and one HPC containing silica fume were included in the test matrix. Parallel laboratory corrosion studies are being conducted on cast-in-place specimens exposed to a simulated effluent. The initial results of the field exposure showing the difference in corrosion protection of reinforcing steel in the four different types of concrete subjected to accelerated curing and conventionally cured are presented. Laboratory results investigating the effect of cracking on the corrosion protection provided by the four types of concrete are also presented. The reinforcing steel corrosion was evaluated using linear polarization resistance (LPR) and the more recently developed electrochemical noise measurement technology. The suitability of these techniques to measure and monitor the corrosion of reinforcing steel in concrete is also discussed.

In this report, freezing and thawing test, carbonation test and length change test were carried out, determine the effects of differences in cement kind and curing methods on the durability of super-workable concrete, focusing mainly on placing during cold weather. Normal portland cement and three kinds of low heat type cement were used. A w/c of 50% was used for the normal portland cement, and a ratio of between 3O~35% for the low heat type cement. The curing methods of the specimens are standard curing, atmospheric curing, site sealed curing, site water curing and heat curing. During freezing and thawing test and accelerated carbonation tests, it was found that when heat curing is employed to prevent initial frost damage, if due consideration is not given to the temperature and wetness conditions of the curing concrete, there are cases where durability may be worsened instead of improved. With regard to the measurement of length change by the test methods adopted in current standards, there is a distinct possibility that the measurement values are not only due to drying shrinkage, but are also strongly influenced by autogeneous shrinkage of the concrete