Journal of Materials in Civil Engineering

Studies related to the durability of bridge deck concrete in the state of Tennessee have been ongoing at the University of Tennessee for the past decade. The most recent phase of this research began in the fall of 2009 with a focus on developing a criteria and methodology to assess the durability of bridge deck concrete in Tennessee. The concrete’s resistance to chloride ion penetration was used to evaluate durability. This resistance was measured by two test methods: the surface resistivity (SR) test and the rapid chloride ion penetration (RCP) test. Current guidelines set forth by the Tennessee Department of Transportation (TDOT) require that a Class D concrete mixture be placed on all bridge deck applications. The SR and RCP tests have been performed on Class D concrete cylinders from various bridge deck placements across the state for the past 2.5 years. The Class D mixture consists of 75% cement and 25% fly ash (generally Class F). Results indicate that the current concrete mixture fails to adequately resist chloride ion penetration at satisfactory levels. Ternary blend concrete mixtures, so defined when the mixture contains three different types of cementitious materials, have been found to offer benefits to both the strength and durability of concrete. Thus, it was decided to propose a ternary blend concrete mixture. While ternary blends are not currently prohibited by TDOT, the Class D concrete mixtures currently being placed on bridge decks are, as noted, binary mixtures. Ternary blend laboratory samples were created to compare SR and RCP values to the typical Class D mixtures. Results from the tests, as well as results reported in technical literature, indicate that ternary blend mixtures have significantly better resistance to chloride ion penetration than the typical Class D mixtures, indicating improvement in concrete durability with such a mixture.

The usage of general mortar for embedding and partially filling units in masonry prisms was evaluated through compressive tests. Filled and unfilled prisms were tested to verify the differences in their compressive behavior. Four mortar mixes with three water/cement ratios for each mix were used in tests. Results indicated small differences between filled and unfilled masonry prisms. Mortar had a slight effect on the compressive strength of the masonry. A more significant effect, however, could be observed on secant elastic modulus, compressive fracture energy and deformations of masonry prisms. An analytical model to represent the stress versus strain diagram of masonry prisms was proposed which depends on the compressive strength of mortar and masonry prisms. Furthermore, results indicate that the use of general mortar for embedding and filling masonry prisms can offer a solution in terms of building technology.

Mortar, as concrete-like coarse-structured materials, has a fracture process zone ahead of crack tip after the crack initiation. The maximum fracture load must be related to the cohesive crack-tip local fracture energy due to the relatively limited crack growth in the critical state. The intention of this paper is to correlate the local fracture energy with the maximum loads in mortar specimens. An analytical approach is proposed on the correlation between the two parameters. Then a fracture test has been performed on three-point-bending notched mortar beams with a wide range of notch depths. Upon comparison of the predicted and experimentally measured peak loads, it is found that the crack-tip local fracture energy indeed varies with notch depth and beam height. Thus, the trilinear model for the local fracture energy distribution is confirmed in mortar specimens, indicating both the front and back free boundary effects. Based on the trilinear model, the size-independent fracture energy can be obtained if the notch depth and the ligament length are long enough. The proposed approach is analytical and convenient without the load-displacement curves in tests.

The susceptibility of stabilized soil (SS) masonry components to forces of degradation is significantly dependent on the choice of constituent materials, production techniques, mode of exposure, as well as the aggressiveness of the medium to which they are exposed. This paper examines the choice of mix design format for SS masonry materials contingent on their weatherability characteristics and analyzes the mechanisms that trigger potential weathering variations. Two reproducible model soils (sandy loam [SL] and silty-clay loam [SCL]) in the presence of a variety of stabilizers, pressed at $6\mathrm{N}/{\mathrm{mm}}^2$ into blocks, applied two curing routines, and measured weight loss following two forms of water-based degradation were used in the study. The test program shows remarkable potential for erosion resistance of SL-cement and SCL-lime mixtures that reflect the inherent variability in the material composition, nature of soil-stabilizer composites, and technique of exposure. The relevance of the weatherability study in the use of SS-based materials in the humid tropics demonstrates innovative and improved use of materials through clearly defined performance indicators and offers capability for retention of desirable properties like restrained configuration and attractive appearance in the building envelope, which otherwise would have been compromised.

This paper reviews recent studies on preparation, hydration, and properties of magnesium phosphate cement (MPC). MPC is the phosphate-bonded inorganic material derived from reactions between phosphate and magnesium oxide. The hydration reaction in the $\mathrm{MgO}\text{-}{\mathrm{NH}}_4{\mathrm{H}}_2{\mathrm{PO}}_4$ system is strongly exothermic, and the main product is struvite (${\mathrm{NH}}_4{\mathrm{MgPO}}_4·6{\mathrm{H}}_2\mathrm{O}$). The setting time and mechanical properties depend on the proportion and characteristics of raw materials, water to binder ratio, the addition of retarders, and admixtures. Moreover, the MPC demonstrates favorable durability performance compared with Portland cement. Additionally, recommendations for future research are proposed.

As one of the most important and expensive investments/assets in modern society, asphalt concrete pavements age and deteriorate with time as a result of asphalt mixture aging, cumulative loading, environmental conditions, and/or inadequate maintenance. The detection of pavement health condition is very important for a pavement analysis and management system. In this paper, a pavement health monitoring system was developed based on an embedded sensing network with an efficient combination of various commercial pavement sensors. The collected pavement responses were clear and reasonable and compared with a numerical simulation. The modulus of the pavement surface layer can be back-calculated every year or every several months based on testing runs and numerical models. Fatigue cracking and rutting models were selected to predict the distress of the experimental section according to the actual strain measurement from each passing vehicle. A health monitoring system, which contains the continuous monitoring and periodic testing as routines, is proposed as an important component of a pavement management system.

This paper investigates the use of glass cullet as a 100% sand replacement in Portland cement concrete (glasscrete) systems. Specifically, this paper evaluates the fresh and hardened properties of these systems in comparison with conventional natural sand concretes on the basis of similar 28-day design compressive strength, or the same w/cm. The results show that glasscrete mixtures need a lower w/cm to match the 28-day compressive strength of conventional concrete. In addition, glasscrete mixtures have greater elastic modulus, less drying shrinkage, less water sorptivity, and greater resistance against chloride ion penetration. Empirical curves are developed to provide material engineers and suppliers with necessary design specifications on the proper w/cm to implement when proportioning glasscrete mixtures. This study concludes that glasscrete mixtures are producible with adequate consistency and mechanical and durability performance, as long as the alkali-silicate reaction is properly controlled using pozzolanic materials.

This paper describes the development of high-performance fiber-reinforced concrete (HPFRC) with very high strength and the feasibility of using this concrete as a repairing material. Initially two HPFRC mixtures were developed and cured using four different curing conditions. Compressive strength and flexural strength were determined for those eight combinations. Compared to high-performance fiber-reinforced cement composites (HPFRCC), the increase in compressive strength was in the range of 25–105%. Flexural strength was found to be similar to that of HPFRCC. Based on these strength results, one mixture proportion and two curing conditions were further selected for three bond tests, i.e., direct shear, slant shear, and pull-off. The results showed comparable bond strength in case of direct shear, 20% increase in slant shear, and 40% increase in pull-off when compared with other similar studies.

To address the ever-increasing quantity of scrap tires produced in the United States, a study is conducted on the use of crumb rubber in concrete for enhancement of structures against blast effects. Crumb-rubber concrete (CRC) is produced by replacing a volume percentage of the traditional coarse and/or fine aggregate with crumb-rubber particles. Crumb rubber is produced in various gradations from used vehicle tires. The research program characterizes the mechanical properties of CRC and provides an assessment of the capability of CRC in providing flexural resistance for structural applications. The experimental and analytical investigation found the following four results: (1) crumb rubber replacement of coarse and fine aggregate is done at a cost premium of approximately 0.75 times the replacement percentage; (2) the addition of crumb rubber results in a decrease in unit weight, compression strength, splitting tensile strength, and elastic modulus, which are linearly related to the addition of rubber; (3) the modulus of rupture was not sensitive to replacement of up to 40% rubber aggregate; and (4) flexural failure modes occur at lower demand levels due to the use of rubber replacement. The reductions are consistent with the material property conclusions previously discussed.

The paper presents the results of an experimental program to evaluate the viability of concrete made when various ratios of coarse natural aggregates (CNAs) are replaced with coarse recycled concrete aggregates (CRCAs), coarse recycled ceramic masonry and mortar aggregates (CRMMAs), or both. Results show that incorporation of CRCA and of CRCA and CRMMA simultaneously has no effect on compressive strength. However, this property decreases when only CRMMA is incorporated. A reduction of 23.6% in compressive strength was obtained when 50% of CRMMA was used. Splitting tensile strength is unaffected by incorporation of CRCA but it is affected by incorporation of CRMMA. The mixes with 50% of CRMMA showed a reduction of 20.1% in tensile strength. Every recycled aggregate concrete type suffered a linear decrease of modulus of elasticity as the replacement ratio of CNA by coarse recycled aggregates increased. The use of 100% CRCA caused a decrease in modulus of elasticity of 30%. In the mixes with 50% of CRMMA that decrease was 22.2%. Shrinkage was significantly affected by incorporation of course recycled aggregates, although the degree of shrinkage varied in accordance with their nature and incorporation ratio. For replacement ratios between 50 and 100%, the difference between a reference concrete (RC) and the mixes with CRCA remained constant, inside a 30% increase range.

An experimental investigation of an innovative recycling method to reuse dredged sludge in asphalt pavements is presented. According to this method, semifinished products or agglomerates, made of dried sludge and bitumen, are produced. These products may be used to partially substitute fine sand and bitumen in the asphalt mix. In this paper, the practical aspects of the manufacture, storage, and transportation of these agglomerates are simulated in order to demonstrate the feasibility of the method. The technical properties of asphalt mixes prepared with these new products are compared to those of a reference asphalt mix, in terms of Marshall characteristics, stiffness, complex modulus, permanent deformation, and water sensibility. Environmental and economic issues are also analyzed. A simplified cost factor analysis shows that this method is economically advantageous compared to the disposal of contaminated sludge.

Lightweight cellular cemented clays have wide range of applications in the infrastructure rehabilitation and in the construction of new facilities. Since the inception of this method, the developments in the plant and machinery as well as associated field techniques have surpassed the basic understanding of strength developments in lightweight cellular cemented clay. In this paper, an attempt is made to identify the dominant parameter, governing the unit weight, strength, and compressibility characteristics of lightweight cellular cemented clay, which helps control input of water, air foam, and cementing agent to attain unit weight and strength development with curing time. From this research, it is discovered that water-void/cement ratio, $wV/C$ is the dominant parameter for the above purposes. From the critical analysis of test results, a mix design method to attain the target strength and unit weight is suggested. This method is useful from both engineering and economic perspectives.