Journal of Materials in Civil Engineering

A chemomechanical mathematical model is presented to simulate the response of concrete exposed to external sulfate solutions. The model is based on the diffusion-reaction approach, and several mechanisms for the reaction of calcium aluminates with sulfates to form expansive ettringite are considered. Fick’s second law is assumed for diffusion of the sulfate ions. A second-order chemical reaction between reacting calcium aluminates and ingressing sulfates depletes the sulfate concentration. The products of the second-order reaction between the aluminates and sulfates are chosen among several competing mechanisms, and a rule-of-mixtures approach is used to relate the expansive nature of the products with the prescribed specific gravity of the compounds. It is furthermore assumed that the crystallization pressure of products of reaction results in a bulk expansion of the solid. The constitutive response of the matrix and the expansive stresses are calculated from the imposed volumetric strain. Microcracks are initiated when the strength of the matrix is reached, leading to changes in the diffusivity and a reduction in the elastic properties of the matrix. The variation of diffusivity is linked to the scalar damage parameter due to cracking of the matrix. Due to the changes in the diffusivity, the problem is treated as a moving boundary problem, and a methodology is proposed to adapt the solution of the 1D case to the 2D problem of a prismatic specimen. Theoretical expansion-time responses are obtained and compared with a variety of data available in the literature.

A study is presented to predict the degradation of cement-based materials due to external sulfate attack. Parameters of the model are chosen based on the mix design parameters, degree of hydration, and exposure conditions of concrete. A solution of the diffusion equation with a term for a second-order chemical reaction is proposed to determine the sulfate concentration and calcium aluminate profile as a function of time and space. The crystallization pressure of hydration products such as ettringite can lead to internal stresses. Using the volumetric information, the model predicts the generation of internal stresses, evolution of damage, reduction in stiffness, and thus expansion of a matrix phase. The theoretical expansion-time responses are obtained and compared with a variety of available data in the literature. The most important parameters are the w/c ratio, internal porosity, diffusivity of the cracked and uncracked material, and available calcium aluminates. The importance of controlling the pH of the test solution is clearly observed. Model simulations indicate a reasonable agreement with experimental expansion-time data available in the literature.

Some lead alloys have compressive elastic and creep properties that make them potentially useful in certain types of structures, but until now very little useful mechanical property data have been available. Results from short-term compressive stress-strain and from longer-term creep tests are presented for three standard lead alloys and “pure” lead in a format that it is hoped will be of use to structural designers. The stress-strain results show that work hardening improves the short-term elastic behavior of the lead alloys tested, and indicate that of the alloys tested, copper tellurium alloy is the most stable. The compressive creep results show that it would normally be acceptable to ignore primary creep and just include secondary creep in analyses. Two forms of creep equations are presented for use in analyses, but care is needed when using these, since in certain cases they can produce a strain rate value significantly different from that measured.

Two-stage concrete is made by packing the forms with coarse aggregate and then pumping in a cement-based grout to fill the voids. The two-stage concrete is characterized by a higher proportion of coarse aggregate. As the coarse particles are in close contact, the applied load is transmitted from particle to particle while the grout is simply filing in the interstices. Thus, the mechanical characteristics of the two-stage concrete in failure conditions are distinctly different from those of ordinary concrete. Contrary to the ordinary concrete, there is no background information for evaluating the two-stage concrete elastic modulus. This paper presents the results of some experimental tests of three types of coarse aggregates and three different mix proportions of grout. Stress-strain relations in the function of water-cement and cement-sand ratios are elaborated. A relationship between the elastic modulus and the compressive strength of two-stage concrete is statistically derived.

One of the ways in which highly urbanized cities cope with increasing amounts of municipal solid waste (MSW) generated by the population is incineration. As land is a very precious commodity and landfills are fast dwindling in most highly urbanized cities, the disposal of the ash generated from MSW incineration poses increasingly difficult problems for the municipalities. A viable solution to the disposal problems would be the reuse of MSW ash for civil engineering applications. A research study of the properties of the incinerator fly ash derived from MSW incineration indicated that fly ash is a potential source of jet-grouting admixture for soil improvement. The fly ash exhibits a likelihood of pozzolanic reaction due to its chemical composition and physical characteristics. The use of fly ash as an admixture in the stabilization of a soft marine clay resulted in stabilized samples with an improved strength more than 75 times that of the untreated clay. Incorporation of fly ash also improved drainage property by at least one order of magnitude and reduced both the plasticity and compression indices by about 69 and 23%, respectively. Leachate investigation conducted on the fly ash–stabilized soils indicated that chromium was well-below the World Health Organization drinking water limit, while nickel and lead were in excess of the limits. The nickel and lead leachate concentrations diminished to below the acceptable drinking water limits over a period of about 130 and 110 days, respectively.

Investigations have been conducted during the last three decades regarding chloride penetration and prediction of corrosion initiation. However, few investigations have dealt with corrosion propagation and/or residual life predictions, which are also needed for durability forecasting. Therefore, the aim of this investigation is to discuss, based on experimental information from previous investigations, the possibility of linking the degree of degradation (from a load-capacity reduction point of view) to the surface distress (for example, crack width opening) of a corroding reinforced concrete element in a marine environment. An empirical relationship between the residual load capacity of a reinforced-concrete element and the degree of reinforcement radius loss by corrosion was estimated, and a second empirical relationship between the surface crack width and the reinforcement radius loss was established based on available experimental data. Finally, data between the average corrosion penetration and the maximum pit depth were used to propose an empirical relationship that may be applicable to the performance of corroding prestressed-concrete elements.

Ettringite and thaumasite can be found among the deterioration products of cementitious materials exposed to sulfate and hydrochloric attack. The results of a test program to investigate the acid resistance of self-compacting concrete (SCC) and conventional concrete (CC), immersed up to 18 weeks at 20°C in sulfuric and hydrochloric acid solutions, are described. The SCC was prepared with 47% carboniferous limestone powder, as a replacement for cement, and an ordinary portland cement. The CC was prepared with portland cement only. The water-binder ratios of the SCC and CC were 0.36 and 0.46, respectively. The parameter investigated was the time, in weeks, taken to cause 10% mass loss of fully immersed concrete specimens in a 1% solution of sulfuric acid and the same amount of loss in a 1% solution of hydrochloric acid. The investigation indicated that the SCC performed better than the CC in sulfuric solution but was slightly more vulnerable to hydrochloric acid attack compared to CC. The mode of attack between the two solutions was different.

This paper examines the ability of carbon fiber reinforced polymer (CFRP) wrapping to enhance the bond of corroded reinforcing steel bars in concrete. Thirty-two bond pullout specimens were considered. Test variables included the clear concrete cover (15, 30, and 60 mm or 0.6, 1.2, and 2.4 in.), degree of corrosion (0, 1, 5, 7, and 10% mass loss), and presence or absence of transverse CFRP wrapping. The specimens consisted of a concrete prism measuring $150\times 150\times 200\mathrm{mm}$ $(6\times 6\times 8\mathrm{in}\text{.})$ with a No. 10 M reinforcing bar placed in the corner of the prism. The specimens were constructed with 3% ${\mathrm{Cl}}^{-}$ by weight of cement premixed in the concrete to depassify the tensile reinforcing steel. The specimens were placed in a constant high-humidity environment, and corrosion was induced by means of an impressed current. Following corrosion, the specimens were tested by bar pullout to determine the bond strength versus slip of the reinforcing bars. The bond strength of the reinforcing bars in the concrete prisms increased at a small level of corrosion, but decreased as the degree of corrosion increased. The failure mode typically was bond splitting in unwrapped specimens. Strengthened specimens exhibited an increased bond strength and failure by bar pullout due to the confining effects of the CFRP strengthening.

In this paper, the damage in concrete around a reinforcement bar is examined, and three types of damage in concrete and at the concrete-rebar interface are defined. Based on these definitions, a three-dimensional damaged reinforced-concrete (DRC) element is proposed. The element consists of a 10-node concrete element, a two-node rebar element, and a four-node concrete-rebar interface element. Experiments were carried out to obtain the parameters for the bond damage evolution equation. The proposed DRC element is implemented as a user-defined element of MSC MARC2000, a commercial finite-element analysis software package. Two numerical examples were examined, and the results show that the DRC element can simulate the bond deterioration in reinforced-concrete structural members with sufficient rationality, accuracy, and efficiency.

This paper presents laboratory experimental results on new Fabry-Perot fiber-optic sensors to verify their behavior and applicability for strain monitoring of engineering materials and structures. The research program consisted of thermal tests, tensile tests, and flexural tests. Two types of Fabry-Perot fiber-optic sensors were investigated and compared to electrical resistance strain gauges and fiber Bragg gratings. Experimental results show that Fabry-Perot fiber-optic sensors perform linearly in monitoring tensile and compressive strains of infrastructure elements, and demonstrate good response to thermal variations and static and dynamic loading conditions. The fiber-optic sensing technology shows an enhanced accuracy and has potential for significant improvement in long-term strain monitoring over conventional strain gauges in field applications.

Premature deterioration of concrete structures has created awareness and concern about the durability of concrete. Concrete mixtures used in the construction of residential basement walls and foundations have a high water to cement (w/c) ratio $(w/c>0.6)$ and low cement content $(<280\mathrm{kg}/m^3)\text{.}$ The result is friable concrete with a highly porous surface layer and high potential for cracking. The defects have a direct impact on the durability of concrete. This experimental study examines the effects of three parameters—mix design, formwork, and consolidation—on the quality of the surface of high w/c concrete. The fresh concrete is characterized using its rheological properties—in particular, its yield stress and plastic viscosity. Pulse velocity, pull-off strength, and compressive strength were measured to evaluate the quality and the mechanical properties of the hardened concrete. The durability of the hardened concrete was evaluated by measuring its surface transport properties—namely, its air permeability and sorptivity. The results show that it is possible to correlate the rheological properties of fresh concrete to the mechanical and permeation properties of the hardened concrete.

This investigation was performed to develop technology for manufacturing cast-concrete products using Class F fly ash, coal-combustion bottom ash, and used foundry sand. A total of 18 mixture proportions with and without the by-products was developed for manufacture of bricks, blocks, and paving stones. Replacement rates, by mass, for sand with either bottom ash or used foundry sand were 25 and 35%. Replacement rates, by mass, for portland cement with fly ash were 25 and 35% for bricks and blocks, and 15 and 25% for paving stones. Analysis of test data revealed that bricks with up to 25% replacement of cement and blocks with up to 25% replacement of cement and sand with recycled materials are suitable for use in both cold and warm climates. Other bricks and blocks were appropriate for building interior walls in cold regions and both interior and exterior walls in warm regions. Paving stones with 15% replacement of cement with fly ash showed higher strength, freezing and thawing resistance, and abrasion resistance than the control specimens.

The durability of a concrete road to abrasive forces can be assessed effectively by measuring its abrasion resistance. This technical note reports the findings of a laboratory study including compressive strength, abrasion, and porosity properties of concrete mixtures made with fly ash and normal portland cement. The study involves two replacement ratios of fly ash, various water-cement ratios, the use of a superplasticizer, two curing conditions, and four concrete ages. Statistical models that relate abrasion to strength and porosity are presented.