International Concrete Abstracts Portal

This paper provides results of different types of curing in hot weather environment on the compressive strength of concrete made with portland cement and complementary cementitious materials (CCM) such as natural pozzolans, fly ash (FA), granulated blast furnace slag (GBFS), and silica fume (SF). In all concrete mixtures, a superplasticizing admixture (SPA) was used. Nine series of concrete mixture were made. In seven of them (1,2,3,4,5, 6 and 9) the normal portland cement (NPC) content was 200 kg/m3 and in two of them (7 and 8) the same amount of cement was used but it was a portland-natural pozzolan cement (PNPC). The CCM varies from 9.9 to 60.6% of the total cementitious material. The W/C in all series was 0.70 when using NPC or PNPC. The W/C+CM varied from 0.28 to 0.63. In all series the same amount of 1260 kg/m3 of coarse aggregate was used. Five different ways of curing were used. One was the initial and final ASTM curing at 23°C up till the age of testing as reference, and four different ways of curing in hot weather environment at 37°C for the first 24h were used. These final curings were: A) ASTM; F) three day and G) seven-day water spray for 15 minutes every 2h; and (E) covered by two layers of membrane. Adequate compressive strength development (CSD) can be obtained using CCM but very good curing is necessary. Generally, by casting specimens at 37°C and put them under ASTM curing next day at 231t2"C (A), the strength at 28 days was lowered by about 8% and at six months by about 8% lower than these casting at 23°C. Membrane curing was less effective at later ages mainly when fly ash was used. There exist an optimum amount of fly ash to obtain maximum compressive strength at later ages.

High-strength concrete shows particular characteristic behavior at ele- vated temperatures, such as explosive spalling, that is rarely observed in normal-strength concrete. This behavior has been attributed to the very dense concrete matrix usually associated with high-strength concrete. This paper presents the effect of fiber reinforcement on mitigation of explosive spalling and residual properties of high-strength concrete under elevated temperatures (600°C). The experimental work has been carried out on the influ- ence of three parameters associated with fire resistance. These three parameters are an addition of polypropylene fibers andor polymer beads, the moisture content of the concrete and the water to cement ratio. The experimental results showed that the internal temperature elevation was mitigated in the test specimens, that contained the fibers or beads, that were melted by heating, by low cement-water ratio and by high moisture content. The accompanying strains due to heating at these conditions were reduced in the test specimens.

Thermal cracking is a serious problem with modern portland-cement concrete structures, especially cast-in-place massive elements made with relatively high cement content and cured under hot-weather conditions. From theoretical considerations and field experience it is concluded that blended portland-cement concrete mixtures containing 50 percent or more ASTM Class F fly ash by mass of the total cementitious material perform much better under these conditions.

An extensive laboratory program was initiated in the early 1980's to develop high-strength lightweight concrete for use in offshore oil and gas structures in severe marine environments. From the results of that development program, four mixtures were chosen to be evaluated under field conditions. Large prisms (305 by 305 by 914mm) of each mixture were placed in the tidal zone at the U.S. Army Corps of Engineers Severe Weather Exposure Station on the border between Canada and the United States. The mixtures used an expanded slate aggregate from the USA and a pelletized clay aggregate from Japan. All mixtures contained silica fume and had total binder content from 494 to 556 kg/cu m with water-binder ratios of 0.28 by mass. The concrete density varied from 1800 to 1990 kg/cu m, with 90-day strength from 60 to 73 MPa depending on the mixture. The prisms under-went annual visual and non-destructive evaluations. After 10-years exposure in the tidal zone, the prisms were removed to the laboratory where they were examined for strength, robustness and chloride ion penetration. This paper reports the results of the test program. In general, the overall performance looks very good.

An experimental investigation was conducted at the University of Auckland to quantify the performance of shear studs embedded in composite ribbed slabs, formed by casting lightweight polystyrene concrete onto profiled steel decking. In total, 18 tests were conducted using a new type of push-off test rig, with test units composed of either lightweight polystyrene concrete or normal weight con- crete (to facilitate performance comparison). This paper reports and discusses the main results of those 18 tests. Results indicated that in most cases designs utilizing lightweight polystyrene concrete had considerable ductility and shear capacity. Recommended design provisions based on the experimental data are presented.