Journal of Materials in Civil Engineering

Cracking, i.e. material separation at the moment of fracture, is inherently an irreversible process and, hence, is synonymous with material damage. In failure analysis of concrete at increasing applied load, the degree of irreversibility, i.e. material damage, must be capable of being readily quantified by experimentally measurable or mathematically defined quantities. This paper shows the development of a new damage variable to analyze the failure process of a body concrete material, which has an aspect ratio of 2.5, at monotonic uniaxial compression up to the peak load carrying capacity, σ_c,u. This damage variable is derived from the intrinsic characteristics of the microcrack propagation within the bulk concrete material. It is readily quantified by the experimental stress and strain data of a uniaxial compression test to ultimate failure. It possesses the predictive capability to define the degree of damage accumulation within the bulk concrete material at any stage of the applied loading.

This paper reports test results showing how the heating-cooling process like the one occurring during fire action can affect the tensile strength and the strain after rupture of the steels normally used in reinforced and prestressed concrete structures. Laboratory tests were carried out to assess the values of these properties after heating. In these tests, steel samples were heated up to different temperature levels followed by a cooling process. Cooling in the air, cooling by water jet, and cooling by total immersion in water with agitation were the cooling processes used. For temperatures up to 600°C, the tested reinforcing steel showed no major alterations. However, for temperatures above 700°C, important changes in the steel properties could be observed. For the prestressing steel, those alterations began at 400°C.

The Boltzmann-Matano methodology was used to calculate the nonsteady-state chloride diffusion coefficients for blended cement concrete, which incorporated fly ash and ground granulated blast furnance slag. It was found that the chloride diffusion coefficients depend on time and concentration/depth and can be expressed as linear functions of the Boltzmann variable. Furthermore, there was a marked reduction in the chloride diffusion coefficients when the slag content and curing time were increased. The optimum replacement was 65% slag.

A lining system for pipeline rehabilitation uses the method of deforming then reforming a conventional polyethylene pipe to allow installation inside an existing pipe. The liner pipe can be structurally designed as a flexible pipe using existing field and operating conditions. One of the important design factors is its wall buckling under short-term external loads, such as those resulting from floods, sudden increase of soil pressure, or sudden drop in internal pressure. This paper examines some of the buckling formulas introduced by various researchers, and proposes a simplified design methodology based on experimental research for estimating critical buckling pressure under short-term external loads. Considerations are given in this method to liner thickness, diameter, standard dimension ratio (SDR), and stresses induced by manufacturing and installation processes.

Plain rebars are often used in precast concrete elements. The provision of plain rebars along either side of the precast joint will strengthen its resistance and provide greater ductility. However, to fully utilize plain rebars as reinforcement for concrete, some aspects of their behavior have to be determined, including bond and anchorage in concrete. In this paper, the bond strength of plain rebars in concrete is studied. Results of pullout tests on short lengths of plain and deformed rebars in concrete are presented. The effects of rebar type, rebar diameter, embedment length, concrete strength, and loading rate on the bond behavior are examined. It was found that (1) the bond strength of plain rebars was only 28.6 that of deformed rebars; (2) the slip at failure was greater for the plain rebars than for the deformed rebars; and (3) increasing the concrete compressive strength was able to improve the bond properties.

This technical note presents results of an experimental program carried out to analyze the influence of protective coatings on the bar-concrete bond. The value of the bar-friction coefficient is obtained by testing a concrete tension strut reinforced with only one steel bar. The proposed experimental technique is described in detail, and typical results for smooth and ribbed bars are given. The experimental program compared manually applied epoxy and zinc coatings, and 72 tension strut tests were carried out. Statistical analysis shows a significant influence of the type of coating on the steel-concrete bond.