Journal of Materials in Civil Engineering

This paper describes an investigation of improving the bond strength of masonry mortars through the use of polymer additives, so that more efficient use of unreinforced masonry may be realized. A brief description of the mechanisms involved in polymer-modification of cementitious materials is provided as background for the experimental program. Results from a clay brick, type S cement-lime masonry mortar bond strength testing program investigating various admixtures are presented. The admixture treatments include numerous latexes, a defoaming agent, and a superplasticizer. Test specimens were cured under both moist and dry conditions. Very significant increases in bond strength were realized through the addition of several polymers, a plasticizer, and combinations of polymers and the plasticizer.

Asphalt cement is a rheological material because its deformation characteristics vary not only with load but also with rate of load application. The chemical composition of asphalt cement affects its behavior. One of the methods that has been developed to study the molecular structure of materials is high pressure-gel permeation chromatography (HP-GPC). In this paper, the possibility of using the HP-GPC chromatograms to predict asphalt rheological properties is evaluated. Mathematical models are generated to predict the rheological properties of asphalt cement based on its molecular size. In the Gulf countries, there are currently four asphalt-producing refineries that include Ras Tanura and Riyadh refineries in Saudi Arabia, Al-Ahmadi refinery in Kuwait, and Bapco refinery in Bahrain. The asphalt produced by those refineries is referred to as “Arabian asphalt.” For this study to be comprehensive, it was decided to collect asphalt samples from all those refineries. Another set of polymer modified asphalt samples with 5, 10, and 15% crumb rubber and 3, 6, and 9% styrene-butadiene-styrene was included in this study to evaluate the effect of polymer modification on the molecular size distribution of the asphalt samples.

Recycling waste materials is a viable solution to the expensive and environmentally unacceptable disposal problem for these products. Approximately 9,500,000 tons of roofing shingles are produced each year. The cost is between $18 and $60 per ton to dispose of these materials. Reclaimed roofing shingles contain hard crushed aggregate, high viscosity asphalt, and fibers that may be desirable for the production of hot mix asphalt (HMA) pavements. One source of roofing shingles was evaluated for use in HMA mixes. The roofing shingles used were 100% manufacturer's postproduction fiberglass shingle scraps. The properties of the HMA mixture with shingles were evaluated and compared with conventional (no shingle) HMA mixture. The amount of roofing shingles that can be added to HMA mixture is limited by the high percentages (−0.075 mm) of materials found in the roofing shingles. A softer virgin asphalt binder should be used to account for the much stiffer asphalt in the roofing shingles. The properties of shingle HMA mixture can be comparable to the properties of conventional HMA mixtures. In addition, shingle can be used in stone mastic asphalt mixtures. Even with shingle added, the stone mastic asphalt may still need a polymer modified asphalt, or fiber, such as cellulose, to control draindown.

Tests conducted to characterize the stress-strain relationship of high-strength fiber concrete in compression using both cylindrical and prismatic specimens are reported. The concrete strength investigated ranges from 70 to 120 MPa. Other parameters include volume fraction of steel fibers and direction of casting in relation to the loading axis. Test results indicate that inclusion of fibers improves the strength and enhances the strain at peak stress but results in a smaller initial tangent modulus for specimens cast in an upright (vertical) position. Vertically cast prisms provide higher strains at peak stress and better postpeak ductility than cylindrical specimens. Based on the test data, an analytical model is proposed to generate the complete stress-strain σ-ε curves of high-strength fiber concrete derived from cylinders and horizontally cast prisms. The proposed model has been found to agree well with the stress-strain curves generated experimentally.

Construction in Saudi Arabia, emanating from rapid development, has caused massive depletion of scarce construction resources. Crushed limestone and sandstone aggregates used in bituminous mixes lack the desirable qualities for proper mix performance. On the other hand, large amounts of steel slag aggregates with good qualities are being produced and put to waste in Jubail, Saudi Arabia. Laboratory evaluation of mixes from steel slag aggregates was done by reconstituting mixes based on Ministry of Communications, Saudi Arabia, and Strategic Highway Research Program specifications. Steel slag and limestone aggregates were proportioned in the sand and filler portions. Treatment was done using portland cement, lime, polymer, and amine additives. The mix properties tested include resilient modulus, split tensile strength, stability, fatigue, and permanent deformation. Analysis of the results showed that mixes with slag in the coarse portion and limestone in the sand and filler portions modified with polymer had high resistance to rutting and fatigue failure.

The effectiveness of concrete surface treatment materials such as silanes, siloxanes, etc., in preventing concrete deterioration due to sulfate attack, carbonation, and chloride-induced reinforcement corrosion was investigated. The effectiveness of these materials in decreasing the sulfate attack was evaluated by measuring the reduction in compressive strength. The chloride diffusion in the coated and uncoated concrete specimens was also evaluated. The performance of these materials in reducing carbonation was studied by exposing the coated and uncoated concrete specimens to a saturated carbon dioxide environment. The reduction in compressive strength due to sulfate attack in the concrete specimens coated with silane/siloxane in conjunction with an acrylic topcoat was very low compared with that in the uncoated concrete specimens and those coated with other surface treatment materials. the chloride diffusion was also least in the concrete specimens coated with silane/siloxane followed by a topcoat. Among all the surface treatment materials tested, silane/siloxane with an acrylic topcoat and two-component acrylic coating were most effective in preventing carbonation of concrete. Furthermore, silane and silane/siloxane with a topcoat were effective in reducing chloride-induced reinforcement corrosion in in-service structures.

Steel ribbed bars with low carbon content and higher ductility, having different chemical composition and mechanical properties, and produced by a different manufacturing technique called the tempcore process, were used to reinforce concrete. The bar exhibited necking down and cup and cone failure in tension test at ultimate load, similar to those observed in the case of mild steel plain bars. Eight concrete beams reinforced with such bars were fabricated and tested under monotonic loading to study the flexural behavior of the beams. Tested beams exhibited large deflection as well as support rotation to such an extent that one of the bars in a tested beam displayed necking down at ultimate load. Fatigue tests on concrete beams reinforced with high-ductility bars were conducted in a systematic manner, by designing the beams on a rational basis for two million load cycles and testing the same using a computer-controlled, servo-hydraulic, closed-loop testing system. An innovative and low-cost measuring technique was adopted to measure the deflection and crack width under running condition of the test. Fatigue tests have disclosed for the first time that the mode of loading also influences the fatigue behavior of beams. This paper presents a complete description of the experimental investigations carried out under both static and cyclic loadings. Observations made on the fatigue life, midspan deflections, and crack width, under both static monotonic and cyclic loadings, are also included. In the case of the fatigue test, percentage increase in deflection, crack width, and curvature over the initial values, due to the type of loading, are also discussed in the paper.

Styrene-butadiene-styrene (SBS) polymer modified binders consist of two-phase (polymer-rich and asphaltene-rich) mixtures. This type of system is thermodynamically unstable, and a phase separation may occur under the influence of gravitational fields. In this study, the phase separation was determined by a hot storage test and characterized using the softening point, dynamic mechanical analysis (DMA), and Fourier transform infrared (FTIR) spectroscopy. Based on DMA and FTIR, influences of the type of base bitumen and the characteristics and concentrations of SBS polymers were studied. In addition, the rheological properties of the separate phases were investigated, and the mechanism of phase separation was discussed.

A mathematical model is established for chloride penetration in saturated concrete. The model takes into account various influential parameters such as water-to-cement ratio, curing time, types of cement, and aggregate content. Two material models are developed for binding capacity and chloride diffusivity, which have a dominant effect on the chloride diffusion process. The chloride binding capacity is modeled by means of the chloride adsorption isotherm. The chloride diffusivity is modeled by a composite material theory in which concrete is considered as a two-phase material with the cement paste as one phase and the aggregate as another. To take into account the effect of aggregate content, the three-phase model for diffusivity of a two-phase composite developed by Christensen is used. The diffusivity for cement paste is characterized by the Kozeny-Carman model as modified by Martys et al. The influences of temperature and chloride ion concentration are also handled in the model. The model prediction agrees quite well with available test results.

A long-term investigation into the drying shrinkage of concrete exposed to natural weather conditions in Kuwait was undertaken. Fifty-two concrete mixes were prepared, and prisms were made and exposed to natural weather after a 28-day period of laboratory curing (water and/or air curing). Parameters investigated included water-to-cement ratio, type of cement, type of admixture and dosage, type of pozzolanic material, water curing period, and type of curing aid and special coating. The admixtures included normal and high range water reducers, and retarders. No adjustment was made on the initial concrete mix proportions when an admixture was added. Drying shrinkage measurements up to a maximum age of 726 days are reported. The results indicated that the drying shrinkage of concretes made with the various admixtures fell within a narrow band, indicating that no particular admixture had a severe negative effect on the concrete. However, the effect of admixture dosage needs further study. Also, the inclusion of either silica fume or pulverized fuel ash, or the use of white cement in the concrete, resulted in a lower drying shrinkage. However, there was no specific pattern for the drying shrinkage results when the water-to-cement was varied. Finally, some of the curing compounds/aids and special coatings used were more effective than others in reducing the drying shrinkage.

Methods of interconversion between relaxation modulus and creep compliance for linear viscoelastic materials are discussed and illustrated using data from asphalt concrete. Existing methods of approximate interconversion are reviewed and compared for their approximating schemes. A new approximate interconversion scheme that uses the local log-log slope of the source function is introduced. The new scheme is based on the concept of equivalent time determined by rescaling the physical time. The rescaling factor, which can be interpreted as a shift factor on a logarithmic time axis, is dictated by the local slope of the source function on log-log scales. The unknown target function at a given time is obtained by taking the reciprocal of the source function evaluated at an equivalent time. Although the method is developed using a mathematical relationship based on the power-law representations of relaxation modulus and creep compliance, the method is not limited to material functions characterized by power-laws but can be applied to general, non-power-law material functions as long as the relevant material behaviors are broadband and smooth on logarithmic scales. The new method renders good results especially when the log-log slope of the source function varies smoothly with logarithmic time.

The main possible physical mechanisms of drying creep of concrete under compression and tension and their limitations are considered herein. The phenomenological approach describing drying creep of concrete as a sum of shrinkage-induced creep and creep-induced shrinkage, presented by the writer in a previous work, is revised and corrected. In view of the new data, the experimental results obtained for load-free sealed concrete specimens subjected to drying prior to sealing indicate swelling behavior due to the change of vapor pressure above water menisci. Such a swelling deformation should be subtracted from the basic creep strain measured in sealed specimens. After this correction, the curve of drying creep under tension loses its “abnormal” character and becomes the regular drying creep curve. The mechanism of drying creep based on the stress-induced shrinkage is called into question, because the corrected drying creep strain represents the extra creep (but not the extra shrinkage) component within the whole range of loading duration.