International Concrete Abstracts Portal

In this paper, the calcium chloride resistance of concrete containing a low dosage of an expansive additive was investigated in comparison to that of plain concrete. To evaluate the chloride resistance, the length of change and compressive strength, EPMA and SEM were used. In addition, comparisons with previous results on chloride resistance of concrete with ordinary expansive additive were also confirmed.

The Ontario Ministry of Transportation has a mandate to specify cost-effective methods and materials for the construction and maintenance of provincial highway structures. In support of this mandate, the Bridge Durability Work Group initiated a performance evaluation of epoxy-coated reinforcement (ECR) in the Ontario bridge environment. Findings of the investigation, which are summarized in this report, strongly indicate that the long-term performance of the ECR is not likely to provide the corrosion resistance or associated maintenance free service life that was originally anticipated by the ministry. Several Ministry structures constructed with ECR have already been rehabilitated, before achieving even a 20-year service life. The paper details the results of numerous in house field investigations to assess the condition of ECR in-service in typical Ontario highway bridges. The paper also presents the findings of field and research studies carried out by independent consultants and academics on behalf of the ministry, to examine ECR performance and to recommend alternative approaches for corrosion protection and structure condition assessment.

The presently standardized ways in Europe to achieve a sufficient durability of concrete for outdoor elements are not always successful. The resistance tests on concretes against single attacks (e.g. frost, frost-de-icing salt, sulfate, alkali-silica reaction) – as they are presently practiced – do not seem to be effective to assess the durability. Also the exami-nation of single specific concrete properties, e.g. permeability parameters, is not an appropriate method. Outdoor elements are exposed to complex environmental influences, i.e. not only to a frost or frost/de-icing salt attack. Likewise, the problem of the alkali-silica reaction (ASR) with alkali-reactive slow/late aggregates is not sufficiently treated. Based on the present state of knowledge the latest approaches in developing performance testing method shall be described. A new type of climate chamber is used to evaluate the durability of concrete for outdoor elements under simulated climate conditions. The principal capability of cyclical storage with alternating temperature and moisture condi-tions in order to achieve an acceleration effect in the simulation of weather conditions on concrete has been proved in previous comparative investigations in our institute. Results of different investigations by means of this new type of climate chamber regarding high performance concrete, normal concrete with different types of cement and ASR-vulnerable concretes will be presented.

In this laboratory investigation, the effects of limestone fillerand granulated blast-furnaceslag (GBFS) additions on the mechanical and durable characteristicsof concrete areanalyzed.The evolution of compressive and flexural strength were determined and,waterabsorptionand sorptivity were used to characterize the permeability of concrete. The chloride penetration under continuous soaking was evaluated using the pounding tests and thesulfate resistance of cement was determined using ASTM C1012 test. The results show that, the complementary behavior of limestone filler and GBFS additions permits to obtainconcrete with strength development similar to portland cement with 35 % less clinker, andthe incorporation of GBFS into the mixtures prevents and improves the inadequateperformance of limestone filler cement in chloride and sulfate environments. Consequently,concretes made with ternary cement offer economic and ecological benefits, with similarstrength evolution and similar or better durable properties compared with binary and plainconcretes. However, to assure the reduction of permeability of concrete an adequate curedtime should be proportionate to assure the hydration progress.

This investigation deals with determining the carbonation resistance of high-volume fly ash concrete. Five air-entrained concrete mixtures were studied consisting of three high-volume fly ash concrete mixtures (HVFA) incorporating 58% of fly ash by mass of the total cementitious materials made with a water-cementitious materials ratio (w/cm) of 0.32, and two control portland cement concrete mixtures, one with a similar w/cm (0.32), and the other with similar 28-d compressive strength as that of the HVFA concrete. Following several curing conditions, some of the specimens were moved to a chamber with 3% CO2 for up to 700 days, and the others were stored in the laboratory environment and/or exposed to the natural environment (without shelter) for more than seven years. The accelerated carbonation test results indicate that for both HVFA and control portland cement concretes, the carbonation depth decreases with an increase in the duration of moist curing from 7 to 28 days. A further increase in the moist curing from 28 to 91 days did not substantially affect the carbonation depth of the control concretes and the HVFA concrete using the high reactive fly ash. The depth of carbonation in concrete was also found to significantly depend on the reactivity of fly ash used; in general, the depth of carbonation deceased with increasing fly ash reactivity. The carbonation results on concrete exposed to natural environment show that the depth of carbonation of HVFA concretes exposed to outdoor environment for seven years ranged from 3.5 to 7.5 mm, and that of the control concrete with a w/c ratio of 0.42 was 2.5 mm. For the control concrete with a w/c of 0.32, the carbonation depth was less than 1 mm. Based on the results obtained, the time required for the carbonation front to reach 40 mm depth in HVFA concrete exposed to the outdoor condition was predicted to be a minimum 240 years. Thus the carbonation is not an issue for HVFA concrete due mainly to its low w/cm and dense structure.