Journal of Materials in Civil Engineering

This paper deals with durability characteristics and compressive strength of soil cement after prolonged exposure to saline ground water. The study was confined to three A-2-4 soils. In the analysis of the results the writers emphasize the utilization of compressive strength as a competent indicator of durability in addition to the conventional percent mass loss. It was found that at early ages compacted soil-cement mixtures continue to gain strength despite exposure to saline water up to about 90 days, then the strength deteriorates. The results also show that with time the residual compressive strength converges to a certain value, after which the rate of deterioration becomes very small. This value occurred at about 270 days for the tested soils. On the other hand, unconfined compressive strength samples immersed in the saline ground water for up to 6 months continued to gain strength, although the gain was very slow beyond 28 days.

The response of five granite stones (fresh or submitted to accelerated aging treatments) to consolidation and hydrofugation treatments has been studied. Changes in free porosity and capillary absorption coefficient (CAC) have been monitored. Statistical analysis of the data indicates an important effect of these treatments on the changes on these physical properties, leading to different fluid-transport capabilities through the stone. Simultaneous hydrofuging and consolidating treatments have a larger effect than any treatment applied separately.

When steel reinforcement corrodes in a concrete structure, the expansion of corrosion products often leads to cracking in the concrete. In this paper, a simple physical model is developed to relate the size of cracks to steel expansion. By assuming the steel/concrete interface to be perfectly smooth or perfectly bonded, upper- and lower-bound solutions can be obtained. The results indicate (1) the presence of an expansion threshold below which no crack propagation can occur; (2) a “pop-in” behavior occurring at a critical expansion that is strongly dependent on initial flaw size; and (3) the steel expansion to generate a given crack size is strongly affected by interfacial bonding. When the theoretical findings are compared to available experimental results, good agreement is obtained. Based on the theoretical results, several guidelines for controlling expansion-induced cracking can be proposed. These include proper control of initial flaw size, addition of fibers to produce an R-curve behavior, and the enhancement of bond and/or friction at the steel/concrete interface.

This research examines the long-term performance of high-density polyethylene liners frequently used in rehabilitating pipeline networks. Buckling of two groups of samples—each consisting of 20 steel pipes lined with HDPE liners—was examined in the laboratory. Group A was subjected to a uniform external pressure equal to about one-half of the buckling pressure, determined experimentally in a similar short-term test. Group B was subjected to one-third to one-fourth of this short-term pressure. Most liners in Group A failed (buckled) prematurely before the required ASTM period of 10,000-h. However, all 20 samples in Group B sustained the applied pressure for over 10,000 h. It was concluded that a design safety factor of 3 to 4 should be applied to short-term pressure to establish the long-term resistance of a flexible liner. Changes in the liner pipe volume with time, under the uniform pressure, were also monitored to estimate long-term creep in the HDPE material.

A nonlinear model for the fracture analysis of high strength concrete members is developed through the interactive use of experimental data and finite-element analysis. The experimentally obtained tensile softening relationship is incorporated into a nonlinear ABAQUS finite-element program. Finite-element analysis is performed to evaluate flexural strength, process zone size, size effect, and the effect of load line deflection measurements on concrete fracture energy. The finite-element model is simple and shown to be successful in predicting beam test results. Finally, the finite-element model is used to compare the size effect model and the two-parameter fracture model. The fracture energies obtained by these alternatives are compared and discussed.

A study on the influence of crack widths and type of bars (plain and deformed) on corrosion of steel bars in cracked concrete is presented here. Microcell and macrocell corrosions of plain and deformed steel bars were investigated on 10 × 10 × 40 cm single crack specimens with crack widths of 0.1, 0.3, and 0.7 mm. Water-to-cement ratios were 0.3, 0.5, and 0.7. Electrochemical investigations were also conducted on 15 × 15 × 125 cm multicrack specimens with plain and deformed bars. For these specimens, water-to-cement ratios were 0.5 and 0.7 and crack widths were varied from 0.1 to 0.4 mm. After electrochemical investigations, chloride ions in concrete, corroded areas, weight losses, and pit diameters of the steel bars were investigated. The entire study was carried out in an artificially created chloride ion-induced corrosion environment. The study concludes that the relationship between crack widths and corrosion rate is observed at the very early age of exposure. Water-to-cement ratio and corrosion rate relationship is clearer than crack widths and corrosion rate relationship. Deformed bars are more prone to corrosion than plain bars.

The use of ground-penetrating radar as a nondestructive investigative technique has gained increasing acceptance both in the United States and in Europe for assessing the structural integrity of concrete structures. However, without an accurate knowledge of the electrical properties of concrete at radar frequencies, it is difficult to quantitatively assess the results of a ground-penetrating radar survey. This paper reports the simultaneous, but independent, developments of two coaxial transmission line systems at Virginia Tech and The University of Liverpool. Both are designed to measure the relative permittivity and conductivity of concrete over a range of frequencies from 100 MHz to 1 GHz. This paper discusses the development of the two transmission lines, and a comparison of the two methods of measurement and interpretation of results.

The axial-stress–axial-strain and axial-stress–lateral-strain behavior of concrete under active lateral confinement is presented. The uniaxial strengths investigated are 41.9 MPa, 60.6 MPa, 73.1 MPa, and 103.3 MPa. The confining pressures (σ₃) used are 4 MPa, 8 MPa, and 12 MPa. Details of an economical lateral-strain-measuring device used in this investigation to produce accurate and repeatable measurements are presented. For low levels of confinement, the constant in the Mohr-Coulomb failure criterion (k) is shown to be closer to five than the traditional value of four. The axial strain at peak stress is shown to have a strong linear relationship with the level of confinement. Parameter values are suggested for Ottosen's constitutive model based on nonlinear elasticity. It was discovered that descending portion of the nonlinearity index (β) versus the secant value of Poisson's ratio (ν^a) was independent of the uniaxial strength and the level of confinement. A simple model is proposed for the descending portion of the β versus ν^a curves.

Sulfate ions present in soil, ground water, seawater, decaying organic matter, and industrial effluents are known to have an adverse effect on long-term durability of concrete. However, ASTM test methods for predicting sulfate resistance have been criticized for failing to adequately predict field performance. In this investigation, cement pastes were tested by an accelerated test method where pH and sulfate concentration remained constant, conditions that are more representative of field conditions. A total of eight cements were tested: three portland cements (Type I/II, Type III, and Type V); one calcium aluminate cement (CA1); two calcium sulfoaluminate cements (CSA1 and CSA2); and two blends containing calcium aluminate, anhydrite, and portland cement (CAPC1 and CAPC2). After 63 days of exposure to a 4% Na₂SO₄ solution where the pH was maintained at 7.2, sulfate resistance of the cements can be described by: CA1 = CSA2 = Type I/II > Type V > Type III > CAPC2 > CAPC1 > CSA1.

The analysis of creep curves is usually based on the rate process approach originated by Eyring in 1936. The modified Eyring equation predicts that creep rate resulting from the viscous behavior is temperature dependent. All authors have so far assumed that the temperature term in the Eyring equation is time independent. In this paper it is recognized that, during the short period of sudden application of a given load to the material, the inevitable deformation that takes place at the interparticle contact zones will cause a sudden increase in the temperature of these zones. During creep, this excess temperature will dissipate and cause a progressive increase in the viscosity of the contact zones resulting in a decreasing creep rate with time. Based on the foregoing concept a theoretical equation for creep rate dependence on time has been developed. Analysis of the experimental data obtained from the creep test of lime–pulvervized-fuel-ash mixtures shows that the derived equation can only account for the decrease in strain rate during the early stages of creep.

Experimental results are reported on the compressive strength of steel fiber high-strength concrete (SFHSC) subjected to high temperatures. The concrete specimens were preheated to different temperature levels, and the existence of a cooling phase was also considered as a variable. During the heating phase the compressive strength of the SFHSC was shown to be more affected by high temperatures than normal-strength concrete without fibers. In general, a gain was registered in the compressive strength of the specimens after cooling.

Jointing sand is the main component of concrete block pavement (CBP) that promotes load transfer between blocks. Often, when sands are available from various sources, it becomes a difficult task to judge the right source of sand. The paper presents the results of an experimental program, conducted to demonstrate a quick and simple technique, for selecting the right source of jointing sand for CBP. The shearing resistance and dilatancy of three sands, three grades each, were obtained from the direct-shear test. The results thus obtained indicate that coarse and angular sand is preferable.