International Concrete Abstracts Portal

Several incidents of early deterioration of structures have been reported in literature; such incidents have a negative impact. Insufficiencies in the durability design may result from a possible absence of explicit guidelines in design codes and standards that establish a standardized language for building design, construction, and operation. Most design codes and standards, while providing a robust framework for structural capacity and serviceability, do not address durability design to a desirable degree. This study examines and critically reviews the durability design in three international codes: the American, British, and Eurocodes. The study revealed that the European and British standards have comparatively more precise and comprehensive durability provisions, whereas the American code has a larger scope for development. The study introduces a proposal for the improvement of durability design provisions in codes to provide beneficial examples that can assist in the update of upcoming editions of these codes.

Past research showed a correlation between the measured apparent chloride diffusion coefficient determined in accordance with ASTM C1556 and the ASTM C1202 rapid indication of chloride ion penetrability test (RCPT) results. Based on that research, a combination of RCPT and strength criteria was proposed to categorize mixtures based on their resistance to chloride ion penetration. This article proposes specification criteria based on a formation factor to categorize mixtures. The efficacy of using both approaches to categorize 44 concrete mixtures prepared from different portland cements, types and dosages of supplementary cementitious materials, and w/cm is examined. It is found that either approach can be used to categorize mixtures based on their resistance to chloride ion penetration. Specimens from 10 mixtures, moist-cured for over 8 years, were tested for surface and bulk resistivity. The same specimens were immersed in chloride solutions in accordance with ASTM C1556, and chloride-ion contents at specific depths from the exposed surface were measured and compared with the later-age bulk resistivity, early-age RCPT, and estimated formation factor.

Limited research work exists on assessment of punching shear of reinforced concrete (RC) flat slabs made with blended cement incorporating ground-granulated blast-furnace slag (GGBS). This research is aimed at analyzing the punching shear strength of RC flat slabs cast from blended cement having GGBS in different proportions as partial replacement of cement. Four flat slabs supported on the ends were tested under column load such that one flat slab was cast from normal concrete with no GGBS and the remaining three flat slabs were cast with 30, 40, and 50% replacement of cement by GGBS. Experimental punching shear, midspan deflections, strain in the steel bars, and cracking pattern of the slabs were determined. The results of punching shear of flat slabs from the tests were compared with the nominal punching shear capacities proposed by BS 8110, BS EN1992-1-1/EC2, and ACI 318. The provisions of these building codes for the punching shear were observed as safe and conservative for the RC flat slab made from blended cement incorporating GGBS.

This paper presents a portion of a state highway agency pooled fund research project to develop performance criteria for concrete that will be resistant to penetration of chlorides, cycles of freezing and thawing, and sulfate attack. This paper presents the portion of the study pertaining to penetration of chlorides. To simulate standard and service conditions, specimens were subjected to either immersion or to a cyclic wetting and drying exposure in chloride solution. Measured apparent chloride diffusion coefficients, determined in accordance with ASTM C1556, were correlated with results of rapid index test methods that provide an indication of the transport characteristics of concrete. Rapid index test methods included were rapid chloride permeability, rapid migration, conductivity, absorption, and initial and secondary sorptivity. A set of rapid index test methods and specification criteria that can reliably classify mixtures based on their resistance to chloride ion penetration are proposed.

Little research is reported in the literature on the effect of pozzolans such as silica fume on structural behavior of reinforced concrete, namely on bond and anchorage characteristics of reinforcing bars in concrete. The objectives of the study were to investigate the effect of silica fume on bond and anchorage characteristics of reinforcing bars in high performance concrete, to study the validity of the upper limit of 70 MPa (10,000 psi) imposed by the ACI Building Code 318-95 on the concrete compressive strength for determination of development length, and to evaluate the reliability of the empirical equation of Orangun, Jirsa, and Breen in estimating the bond strength of deformed bars embedded in high-strength concrete. Sixteen beam specimens were tested. Each beam was designed to include two bars in tension, spliced at the center of the span. The splice length was selected so that bars would fail in bond, splitting the concrete cover in the splice region, before reaching the yield point. The beams were loaded in positive bending with the splice in a constant moment region. The variables used were the percentage replacement by weight of cement by silica fume, casting position, and the superplasticizer dosage. Test results indicated that replacement of 5 to 20 percent of the cement by an equal weight of silica fume resulted in an average 10 percent reduction in bond strength regardless of casting position or the superplasticizer dosage used.