International Concrete Abstracts Portal

Polypropylene and steel fiber reinforced concretes have been used by the author in chemical plant environments since 1980. The applications have been primarily for slabs on grade but have also included grade beams, slab overlays, equipment foundations, pedestals, pump pads, containment barriers, and pile caps. This paper compares durability performance of nonfiber reinforced concrete and fiber reinforced concrete in chemical plant locations in Michigan and Kentucky. The primary durability indicator is crack-free, long-wearing concrete. The results of these durability performances are applicable to the concrete industry in general, and specifically to the placement of concrete in chemical plants. The results indicate that the best durability performance was from concrete reinforced with steel fiber, then polypropylene fiber, and finally nonfiber reinforced concrete. The reasons underlying this performance are explored from the perspective of what is needed for scheduling, cost, and performance of concrete in the various projects, and environments to which the concrete is subjected. This investigation was conducted first by the proper design of the concrete mix proportions, and then by follow-up with field surveys, interviews, and calculations.

With special attention to durability of concrete, the author reviewed the proceedings of the cement chemistry congresses as well as other symposia held during the last 50 years by ACI, ASTM, and RILEM. What is presented here is not a comprehensive progress report on the subject of concrete durability but rather a state-of-the-art report from the author's perspective. It seems that, in spite of some important discoveries valuable from the standpoint of durability enhancement, today more concrete structures seem to suffer from lack of durability than was the case 50 years ago. In order of decreasing importance, the major causes concrete deterioration today are as follows: corrosion of reinforcing steel, frost action in cold climates, and physico-chemical effects in aggressive environments. There is a general agreement that the permeability of concrete, rather than normal variations in the composition of portland cement, is the key to all durability problems. There is also a general agreement that rapid growth of the concrete construction industry after the 1940s led to the production and use of wet concrete mixtures, which are able to meet the strength requirement via a change in the composition of portland cement, but were unsatisfactory from the standpoint of corrosion of reinforcing steel, resistance to freezing and thawing cycles, and chemical attacks. A rise in chemical aggressivity of the environment through the increasing use of deicer salts, and an increase in land, water, and air pollution, has also contributed to concrete durability problems. Although significant advancements have been made in regard to understanding and controlling various physical and chemical phenomena responsible for concrete deterioration, the trend towards less durable concrete structures has yet to be reversed. One of the reasons is that most of the information from tests on durability is in fragmentary form and cannot be easily synthesized into a complete understanding of actual, long-term, effects on field concrete. An over-reliance on test methods and specifications dealing with different aspects of durability has therefore become a part of the problem since accelerated laboratory tests do not correlate well with behavior of concrete structures in practice.

The concrete bridge structural members, called "skew members" (SM), which are positioned from 1.5 m above the sea level to about 20 m down in the sea, and are among the most important elements in bridge construction, were investigated for maintenance purposes after 11 years of service. The underwater arch foundation concrete was also tested. The compressive strength, determined as the average value of 10 concrete cores drilled out from each of two skew members--SM-St. Marko and SM-Mainland--was 62.3 Mpa and 57.4 MPa, respectively. Chlorides had penetrated through the high-alkaline composite by over 20 mm in the splash zone concrete and by over 45 mm in the fully submerged concrete, where {Cl-}-penetration was probably enhanced by hydrostatic pressure. The lack of corrosion of the steel in the concrete, even in the presence of high chloride concentration, could be explained by the absence of oxygen. The gas permeability coefficients Kg determined on the concrete core slices varied in the inner concrete layers of SM-St. Marko from 5.58 to 20.10 x 10-13 cmý and from 0.55 to 2.84 x 10-13 cmý in the concrete at SM-Mainland.

The results of investigation into the erosion-abrasion resistance according to CRD-C 63-80 test method and abrasion resistance according to Bohme test method of steel fiber reinforced concrete specimens are discussed in the paper. Nine mix proportions were used. The water-cement ratios (w/c) were varied from 0.30 to 0.65. The volumetric percentage of hooked steel fibers were varied from 0.25 to 2.0 volume percent at the w/c of 0.30 and at the others the quantity of fibers was constant. In addition, mixes without fibers were made at each w/c. The results show that adding steel fibers to the concrete improves the resistances as measured by both test methods. The erosion-abrasion resistance is improved by an increase of compressive strength and an increase in fiber content. It can be correlated to improvements of abrasion resistance from the Bohme test method but only at constant w/c and different content of fibers.

Seventeen concrete mixtures were prepared to evaluate the deicer salt scaling resistance of some high-strength concretes with a 28-day strength in the 60 to 90 MPa range. A 0.30 water/(cement + silica fume) ratio was used for most of the mixtures and 3 additional mixtures were prepared with a 0.26 water/(cement + silica fume) ratio. In the 0.30 mixtures, two types of cements and a silica fume were used (Type III, Type III + percent silica fume, Type 1 + 6 percent fume), and in the 0.26 mixes, only Type 1 + 6 percent silica fume. Most of the concrete specimens were prepared with different air contents to produce a relatively low spacing factor and a high spacing factor. A very dense dolomitic limestone and a granitic gravel were used as a coarse aggregates. The curing period varied between 1 and 28 days. All the specimen were submitted to 150 daily cycles freezing and thawing in accordance with ASTM C 672, using sodium chloride as a deicer. Weight loss was measured to evaluate the deterioration of the concrete surfaces. The scaling resistance of the specimens made with a Type III cement (with the limestone aggregate or the granitic aggregate) was found to be very good in all cases, irrespective of the length of curing, the silica fume content or the spacing factor values. The non-air-entrained concretes made with a Type I portland cement also had a good scaling resistance after 24 hr of curing but, in this case, a better durability was obtained by using a longer curing period (7 to 28 days). For all concretes, the weight loss after 50 cycles was lower than 0.75 kg/mý and under 2 kg/mý after 150 cycles, and no clear relationship was found between the scaling resistance and the spacing factor. However, there are indications that when a high strength concrete can perform very well in a scaling test without air entrainment, the use of a relatively high air content can somewhat reduce its scaling resistance. Based on these results and others from recent publications, it seems that the use of a water/(cement + silica fume) ratio of 0.30, a good quality coarse aggregate and a portland cement with silica fume generally allows the production of non-air-entrained concretes with a good deicer salt-scaling resistance, even after only 24 hr of curing. It is also possible, with certain Type III cements, to produce deicer salt scaling resistant non-air-entrained concretes without using silica fume.