Journal of Materials in Civil Engineering

Current procedures used to sort round timber beams into structural grades rely on visual grading methods and property assignments based on modification of clear wood properties. This study provides the technical basis for mechanical grading of 228 mm (9 in.) diameter round timbers. Test results on 225 round Engelmann spruce–alpine fir–lodgepole pine beams demonstrate the conservative nature of current timber strength assignments. A good correlation was obtained between static bending strength and static modulus of elasticity (MOE), and between bending properties and dynamic MOE determined in transverse vibration. Relationships were also developed between compressive strength parallel to grain, bending strength, and MOE by transverse vibration. The property relationships developed in this study were used to propose grading criteria consistent with procedures used with mechanically graded softwood dimension lumber. Estimated grade yields obtained using the proposed criteria show that significant increases in yield might be obtained for a specified set of allowable properties than is currently possible by visual grading alone.

The primary objective of this study is to investigate the response of air-entrained concrete to aggressive chemicals. To better correlate to field practices, 60 concrete mixtures were prepared with three cement contents, five air content ranges, and water content adjusted to yield moderate to high slump ranges. Samples were subjected to abrasion testing and were exposed to sulfuric acid, calcium chloride, and ammonium sulfate solutions. The results reveal that air-entrained mixtures yielded reduced permeability but relatively less abrasion resistance. Yet they demonstrated enhanced resistance to chemicals as expressed by more exposure cycles and/or less mass loss. The combined effect of both exposure duration and mass loss is expressed by a factor (chemical disintegration factor), which is thought to be useful in similar studies. The results suggest that producing high workability, air-entrained concrete with adequate strength and abrasion resistance, low permeability, and superior chemical resistance is possible. This can be useful in sewer structures and concrete applications where surfaces are subjected to mild abrasion and aggressive chemicals.

This paper presents the results of a laboratory investigation on tensile strength, bearing ratio, and slake durability characteristics of a class F fly ash stabilized with lime alone or in combination with gypsum. The effects of lime content (4, 6, and 10%), gypsum content (0.5 and 1.0%), and curing period (up to $90\text{days}$ ) on the tensile strength, bearing ratio, and durability characteristics of the stabilized fly ash are highlighted. Unconfined compressive strength test results for the mixes cured up to $90\text{days}$ are presented to develop relationships between different tensile strengths (Brazilian and flexural) and unconfined compressive strength. Both soaked and unsoaked bearing ratio tests were also carried out on this stabilized fly ash. The Brazilian tensile strength of the lime and gypsum stabilized fly ash mixes varied between 309 and $\mathrm{1,084}\mathrm{kPa}$ for $45\text{days}$ curing. The flexural strength of the lime and gypsum stabilized mixes cured for $45\text{days}$ varied between 665 and $\mathrm{1,459}\mathrm{kPa}$ . Fly ash stabilized with lime and gypsum showed medium durability at $28\text{days}$ curing and there was enhancement of durability with increase in curing period. Empirical models to estimate tensile strength, bearing ratio, and slake durability indices of stabilized fly ash from unconfined compressive strength test results are also proposed herein. With enhanced tensile strength and durability characteristics, the stabilized fly ash may find potential use in civil engineering construction.

The objective of this paper is to study the fatigue performance of concrete beams strengthened with carbon fiber sheets bonded by an inorganic matrix. Large size reinforced concrete (RC) beams were strengthened with three layers of carbon fiber sheets and tested under fatigue loading. The relationship between fatigue strength, crack width, and number of cycles was studied and analyzed. Results showed that both load capacity and number of cycles of the RC beams were significantly increased with carbon fiber sheets. The fatigue strength increased by as much as 55% as compared with that of the control beams. Fatigue failure of the RC beams strengthened with carbon fiber sheets bonded with an inorganic matrix started with steel rupturing followed by fiber rupture. It was observed that the fatigue cracks developed during the first few cycles. With increasing number of cycles, the crack width and crack depth increased during the first half million cycles of loading, and thereafter the crack width and depth tended to stabilize.

Soil-cement blocks and cement-soil mortars are used for the load bearing masonry. The paper deals with the scantily explored area of tensile bond strength of soil-cement block masonry using cement-soil mortars. Influence of initial moisture content of the block and block characteristics (strength, cement content, and surface characteristics) as well as composition and workability of cement-soil mortar on direct tensile strength of masonry couplets has been explored. Major findings of this study are (1) initial moisture content of the block at the time of construction affects bond strength and use of partially saturated blocks is better than dry or fully saturated blocks; (2) as the cement content of the block increases, its strength increases, and surface pore size decreases leading to higher bond strength irrespective of the type of mortar; (3) cement-soil mortar gives 15–50% more bond strength when compared to cement mortar and cement-lime mortar; and (4) bond strength of cement-soil mortar decreases with increase in clay content of the mortar. The study clearly demonstrates the superiority of cement-soil mortar over other conventional mortar such as cement mortar. The results of this paper can be conveniently used to select a proportion for cement-soil mortar for soil-cement block masonry structures.

This paper presents a study on cracking risk due to shrinkage of self-compacting concrete (SCC). Cracking of SCC was investigated through a comparison of material properties, such as shrinkage, modulus of elasticity, creep, and fracture parameters, between SCC mixtures and ordinary concrete (OC) mixtures. Restrained shrinkage tests (ring tests) were also performed on the same mixtures. Numerical simulations were then used to assess the correlation between material properties and results of restrained shrinkage tests. SCC and OC were found to have equivalent shrinkage cracking tendency, provided that compressive strength is kept the same and that SCC has adequate segregation resistance.

Rapid industrialization and urbanization in a highly limited land area leads to serious waste disposal problems. Scarcity of land causes the disposal of waste in landfills to be extremely uneconomical. An attractive alternative to waste disposal is conversion of waste into new resources. Past studies have indicated that the conversion of wastes into construction materials is a potential option for management of high volume wastes. However, due to the high processing costs of the wastes, the conversion may not be economically viable. This study examines the detailed thermochemistry of sludge-clay mixes in providing an in-depth understanding of the reactions involved during the process of fusion. Thermal gravimetric analysis detected increased weight loss of the materials around the temperatures of 520 and $900°\mathrm{C}$ , indicating volatilization of organic matter and inorganic salts, at the two respective temperature levels. Differential scanning calorimetry results revealed endothermic reactions, possibly due to dehydroxylation of clay, between temperatures of 480 and $600°\mathrm{C}$ , and calcite decomposition between the temperatures of 680 and $900°\mathrm{C}$ . Intensified endothermic peaks were observed in the mixes of the two materials. Thermal gravimetric analysis–infrared absorption spectrometry revealed increased intensities of the absorption bands at $\mathrm{1,600}{\mathrm{cm}}^{-1}$ at $630°\mathrm{C}$ and $\mathrm{2,900}{\mathrm{cm}}^{-1}$ at $710°\mathrm{C}$ , as a result of the breakdown of organic matter and alkanes, respectively. Energy demand analysis determined the energy required for raising the temperature of each mix to reach each specific temperature. The intrinsic energy required to raise the firing temperature of the aggregates from $400\text{to}900°\mathrm{C}$ was determined to be within the range of 20,347 and $\mathrm{38,254}\mathrm{kJ}∕\mathrm{kg}$ , with 100% sludge exhibiting the lowest energy requirement and 20% sludge exhibiting the highest energy requirement.

Even distribution of aggregate particles in matrices is the target of random mixing processes that are used in the preparation of construction materials to enhance the postplacement uniformity of characteristics. This is particularly important for waste containment barrier concrete where strength, durability, and minimal permeability are desirable. An index, herein referred to as the deviation index (DI) was developed and applied to the cross-sectional areas and volume elements of concrete containing large aggregate to describe distribution deviations of large aggregate particles from perfectly even volumetric distribution. The Poisson distribution and the goodness of fit test were used to describe deviations. Experimental results were obtained from concrete batching tests, designed and performed to compare two mixing methods (rodding and vibration) and a control. The results show no significant uneven distribution as the ${\chi }^2$ values are less than 19.6 at 5% significance level. Within the bounds of these low deviation values, the rodded samples deviated the most, and had the highest DI values (22, volumetrically and 65.32, areally). Sequentially batched samples show minimal variability in DI, indicating that the batch mixing processes were consistent.

A quality control methodology was implemented for aggregate distribution in concrete that can be used in waste containment using the analytical method developed in Part I of this paper. This involves the comparison of three concrete placement methods: rodding, vibration, and placement with neither rodding nor vibration. The concrete mix consists of coarse (#4 stone and #67 stone) aggregate and fine aggregate, the latter of which is sand (making up 29.4% by weight). The experimental results have been used herein to develop quality control charts based on the deviation index, the range of the deviation index within each cylinder, and nonconformity of the aggregate to even distribution, respectively. The nonconformity quality control chart is found to be the most appropriate scheme for evaluating aggregate distribution deviation. The results obtained from the nonconformity quality control chart show that the upper control limit, when specified at three times the square root of the mean deviation index, has a value of 23.4. This is a relatively large value and the deviation indices per slice all fall below it, indicating that the quality of the concrete mix is satisfactory.

Current knowledge on material-related aspects of asphalt recycling with focus on findings from fundamental studies is summarized. By way of introduction, a general description of different types of asphalt recycling methods is given, after which a more detailed compilation of material-related knowledge is presented. Special attention is given to the binder rejuvenation process at asphalt recycling, that is the restoration of reclaimed binder properties. Studies concerning properties of recycled mixtures are also summarized.

When a specimen with symmetrical grooves eccentrically cut on its side surfaces is bent, failure due to the bending-shear combined stress field is induced at the grooved portion, so the failure behavior under various combined stress fields can be examined by varying the location of the grooves. Based on this concept, three-point and asymmetric four-point bending tests using spruce specimens with grooves cut on various locations on the side surfaces were conducted. Bending and shear stresses at the occurrence of failure were calculated based on elementary beam theory, and the test results were compared with three failure conditions: maximum stress, Hill-type, and Goldenblat–Kopnov’s failure conditions. For a rough approximation of the failure behavior, which might be influenced by the loading pattern, the Hill-type condition was superior to the maximum stress condition, whereas Goldenblat–Kopnov’s condition, the expression of which is more complicated, is effective for describing the failure behavior more precisely.

An electrical measurement technique was used to measure the electrical resistivity of cement paste having varying water/cement (w/c) ratios, and consequently the paste properties and characteristics were analyzed. The different hydration periods were identified from the electrical resistivity curve and the differential electrical resistivity curve. The setting time for the samples is reached before the first peak of the differential electrical resistivity curve, and this can provide a new method to determine setting time by using electrical resistivity measurements. The relation between w/c ratio and bulk resistivity at a fixed curing time follows a power law, so electrical resistivity can be used for determination of the w/c ratio in fresh and hardened cement pastes after calibration.

Stabilization of fly ash is one of the promising methods to transform the waste material into a safe construction material. The longevity of lime-stabilized fly ash is related to the amount of lime that remains in the matrix after leaching. This paper presents leaching test results of a class F low lime fly ash stabilized with varying percentages of lime (4, 6, and 10%) alone or in combination with gypsum (0.5 and 1.0%). Addition of gypsum has been found to be very effective in reducing the leaching of lime from fly ash stabilized with lime. The effects of factors like lime content, gypsum content, curing period, and flow period on leaching of lime from a compacted stabilized fly ash matrix are reported herein. Compacted specimens were cured for seven and 28 days. The concentrations of calcium in the effluent emanating from hydraulic conductivity test specimens were measured daily for seven days in succession. The concentration of calcium in the leachate was reduced to 80 from 540 ppm for addition of 1.0% gypsum to fly ash stabilized with 10% lime and cured for 28 days. Two nondimensional parameters ${\alpha }_{\mathit{coi}}$ and ${\beta }_{\mathit{coi}}$ are presented herein to study the effect of gypsum on the total amount of calcium leached out from the compacted stabilized fly ash. A model is also presented to estimate the amount of calcium leached out from the stabilized fly ash.

The main objective of this study is to determine mix design parameters for cold in-place recycling with foamed asphalt. First, the foaming process of laboratory foaming equipment was validated by varying the water and asphalt content. 1.3% water content was adopted to create the optimum foaming characteristics in terms of the expansion ratio and the half-life at 170°C under air pressure of 400 kPa and water pressure of 500 kPa. The mix design was then performed using both the indirect tensile test and the Marshall test for 13 combinations of foamed asphalt content and water content for three different gradations. The water content did not appear to affect the test results significantly. Maximum stability (both wet and dry samples), maximum bulk density, and indirect tensile strength (both wet and dry samples) were all obtained around 2.5% foamed asphalt content. Overall, the highest Marshall stability and indirect tensile strength were obtained in the order of fine, field, and coarse reclaimed asphalt pavement gradations. It is recommended that the indirect tensile strength based on wet samples be adopted for determining the optimum foamed asphalt content.

Results from a series of resonant column tests on two blends of rubber-modified asphalt under varying temperature and pressure conditions are presented. The blends of rubber-modified asphalt tested were samples of Type C, with a 20% rubber content, and Type E, with a 10% rubber content. A sample of conventional asphalt was tested for comparison purposes. These three samples were tested in a resonant column device for their shear moduli and damping ratios under various temperature and pressure conditions to simulate the range of loading environments expected in typical high-speed railway foundations. It is shown that as the rubber content of the asphalt blend increases, the shear modulus and damping ratio of the material increases; additionally, the shear moduli and damping ratios are strongly correlated to changes in temperature. The shear modulus and pressure are related as well, with the stiffness decreasing slightly as the confining pressure is increased; however, temperature effects tend to dominate the behavior of all of the asphalt mixes. Comparing these results to the data from five years ago, there has been little change in the shear moduli of the asphalt samples.