Mang Tia

AN EXPERIMENTAL STUDY ON THE WATER-PURIFICATION PROPERTIES OF POROUS CONCRETE

Abstract The results of an experiment on the compressive strength and water purification properties of porous concrete are reported in this paper. Two sizes of coarse aggregate were used, namely 5 to 10 mm, and 10 to 20 mm. Three absolute volume ratios of paste–aggregate were used, namely 30%, 40% and 50% for a given size of aggregate. The compressive strength is found to be higher when the size of the aggregate is smaller, and when the paste–aggregate ratio (P/G, vol.%) is smaller. In the water purification experiment, the amount of organisms attached on the porous concrete surface is indirectly examined by the consumption of the dissolved oxygen (DO, mg/l). Water purification of the porous concrete is evaluated by the removal amount of the total phosphorus (T-P, mg/l) and total nitrogen (T-N, mg/l). A porous concrete with a smaller size of aggregate and a higher void content was found to have superior ability of the removal of the T-N and T-P in the test water. This is due to the large specific surface area of the porous concrete. Results from this study show that porous concrete using industrial by-products is able to purify water efficiently.

Effect of Early Age Strength on Cracking in Mass Concrete Containing Different Supplementary Cementitious Materials: Experimental and Finite-Element Investigation

AbstractThis paper presents the findings of an investigation using the finite-element method to predict the distribution of temperatures within a hydrating massive concrete element. The temperature distribution produced by the finite-element thermal analysis of the model is used in the finite-element structural analysis to quantify the maximum allowable internal temperature difference before cracking will initiate in the concrete. To verify the results obtained in the finite-element model, four different mixes of concrete, typical for use in mass concrete applications in Florida, were produced and each mix was used to make two large-scale 1.07  m×1.07  m×1.07  m (3.5  ft×3.5  ft×3.5  ft) concrete blocks. The mechanical and thermal properties of early age concrete used values obtained experimentally from the concrete used to construct the four sets of blocks. The temperature distributions produced by the model were shown to be very similar to those measured in the experimental blocks. Results suggest that ...

Rut Initiation Mechanisms in Asphalt Mixtures as Generated Under Accelerated Pavement Testing

The Florida Department of Transportation (FDOT) conducted an experiment to address the effects of polymer modifiers on the performance of Superpave® mixes by using a heavy vehicle simulator. Two fine-graded Superpave mixes were considered. One mix included a virgin binder meeting the requirements of PG 67-22, and the other contained a styrene-butadiene-styrene polymer (SBS)-modified binder meeting those of PG 76-22. Both respective mixes contained the same effective binder content, aggregate components, and gradation. The mixes were designed for 10 million to 30 million equivalent single-axle loads with the use of the standard Superpave mix design methodology. During placement of these mixes, all standard FDOT density requirements and acceptance criteria were applicable. The subsequent investigation showed that the sections with SBS-modified mixture significantly outperformed those with the unmodified mixture. It was also determined that rutting in the unmodified mixture was primarily a function of shear ...

Factors Affecting the Strength and Permeability of Concrete Made with Porous Limestone

An extensive laboratory study was performed to investigate the differences between the properties of concretes made with a porous limestone and those made with a siliceous river gravel and with a dense limestone. The effects of maximum aggregate size, cement type, water-cement ratio, and curing duration were also studied. The results of the study indicate that the concretes made with porous limestone are not significantly different from those made with river gravel. The concretes made with dense limestone show higher strengths and lower permeability than those made with porous limestone or river gravel. Concretes with high strength and low permeability can be produced using porous limestone if the concrete mixture is properly designed.

EFFECT OF AGGREGATE STRUCTURE ON RUTTING POTENTIAL OF DENSE-GRADED ASPHALT MIXTURES

Superpave® mix design, as the name suggests, was developed to provide superior-performing pavements for the transportation industry. However, researchers and designers in their quest to provide such mixtures have encountered problems with some design specifications, such as the restricted zone. Superpave recommends that designers avoid grading through the restricted zone to eliminate tender mixes and gradations that may be too close to the maximum density line. But studies of the performance of the restricted zone have indicated that dense-graded mixtures that violate this requirement have provided good performance. It has also been reported that mixtures that are graded below the restricted zone (BRZ) have poorer rutting performance than those that are graded above the restricted zone (ARZ) or through the restricted zone. It is also known that the minimum voids in mineral aggregates (VMA) requirement, which was established to ensure durability, is very difficult to achieve. It also leads to overasphalting in BRZ mixtures and compromises their resistance to rutting. The effect of aggregate structures on rutting performance of mixtures is examined. Seven limestone and three granite mixtures were used. Six were BRZ mixtures and four were ARZ mixtures. After the behavior of the mixtures was investigated, it was concluded that BRZ mixtures developed different aggregate structures than ARZ mixtures and that the performance of mixtures depended on their aggregate structures. It was observed that the high VMA requirement caused overasphalting in BRZ mixtures, hence their dismal rutting performance compared with ARZ mixtures.

Concrete Containing Recycled Concrete Aggregate for Use in Concrete Pavement

This study evaluated the feasibility of using concrete containing recycled concrete aggregate (RCA) in concrete pavement application. Concrete containing 0%, 25%, and 50% RCA was produced in the laboratory and properties vital to the performance of concrete pavement were evaluated. Results from the laboratory testing program indicate that the compressive strength and elastic modulus are reduced slightly as the percentage of RCA increases. The flexural strength, splitting tensile strength, and coefficient of thermal expansion are about the same for concrete containing virgin aggregate and RCA. The free shrinkage increases slightly as the percentage of RCA increases. With the measured properties, a finite element analysis was performed to determine how the concretes containing the different amounts of RCA would perform if they were used in a typical concrete pavement in Florida. Analysis from the finite element model determined the maximum stresses under critical temperature and load conditions. Potential performance of the pavements was evaluated based on the computed maximum stress to flexural strength ratio. The maximum stress to flexural strength ratio in the pavement was found to stay about the same as the percentage of RCA increases. This indicates that RCA can be used in concrete pavement without affecting its performance.

Alternative solvent for reducing health and environmental hazards in extracting asphalt : An evaluation

Trichloroethylene is a solvent currently used by the Florida Department of Transportation (FDOT) and many state highway agencies for separation of asphalt binders from asphalt paving mixtures in their quality control programs. However, it has been proved that trichloroethylene contributes to ozone depletion, and it is also known to be a carcinogen. The goal of the present study was to determine whether a more environmentally sound and less hazardous solvent could be used for this purpose. The solvent investigated is an n-propyl bromide with the trade name EnSolv. Preliminary studies show that it is safer than many other solvents available today. The study was performed to determine whether EnSolv could be a substitute for trichloroethylene without changing current testing methods. The tests performed included the asphalt solubility test, extraction and recovery of asphalt binders from mixtures, and penetration and viscosity tests with the recovered binders. The results of the study showed that EnSolv could be a suitable replacement for trichloroethylene. In addition, EnSolv could also be recycled and reused in the extraction and recovery procedures.

COMPARISON BETWEEN THE AGING PROCESSES FOR ASPHALT MIXTURES AND THOSE FOR ASPHALT BINDERS

The Strategic Highway Research Program (SHRP) has proposed a short-term oven aging (STOA) process to simulate the aging effects of hot mixing and construction process on asphalt mixtures, and a long-term over aging (LTOA) process to simulate the effects of additional aging of asphalts mixtures in service for 5 to 10 years. In the SHRP Superpav Binder Specifications, the conventional Rolling Thin Film Oven (RTFO) Test is used to simulate the effects of the hot-mix process on a binder, and the Pressure Aging Vessel (PAV) is used to simulate additional aging of the binder in service. This study evaluated the effects of the SHRP STOA and LTOA by comparing their effects on the asphalt binders with those produced by the RTFOT and the PAV processes.

Coarse aggregate effects on elastic moduli of concrete

The results of a laboratory testing program carried out to investigate the effect of coarse aggregate types on the elastic modulus of typical pavement concretes are presented. The elastic modulus was determined in both flexure and compression using static and dynamic means. Three different mixes, made using three different aggregates, were compared. The water-cement ratio was kept at 0.53 throughout the test program. The results showed that within the tested range, the aggregate type significantly affected the studied properties of concrete. Calera aggregate (a dense limestone) with its rough-textured surface and angular shape produced a concrete with higher strength and stiffness than those of concretes made with Brooksville aggregate (a porous limestone) and river gravel. In addition, the measured dynamic modulus in compression was significantly different from that in flexure. Also, in flexure, the dynamic modulus was higher than the static modulus by an average of 23 percent, whereas in compression, th...

Mechanical Properties Assessment of Concrete Containing Reclaimed Asphalt Pavement Using the Superpave Indirect Tensile Strength Test

Concrete mixes containing reclaimed asphalt pavement (RAP) were evaluated by the Superpave Indirect Tensile (IDT) strength test. The IDT strength and elastic modulus from Superpave IDT strength test correlated well with the splitting tensile strength and elastic modulus from the conventional concrete tests. Toughness determined by the area under the stress-strain plot up to the maximum stress was found to be capable of differentiating concretes containing different percentage of RAP. The IDT strengths of concrete were seen to decrease as the percentage of RAP and temperature increased. The addition of RAP in concrete noticeably reduced the elastic modulus but increased the toughness.