Journal of Materials in Civil Engineering

A novel construction unit (Bitublock) composed entirely of recycled and waste aggregates and bound with bituminous binders is currently being developed. At present, the manufacturing process requires the new units to be heat cured to convert the bitumen binder from a viscoelastic material into an elastic-brittle material (known as hardening or bitumen aging). The paper investigates the effect of aging and curing processes on the compressive strength of Bitublocks. In this investigation, samples were compacted at pressures of between 8 and 20 MPa and cured at temperatures of between 60 and $160°\text{C}$ for up to 48 h. Compressive strengths approaching 45 MPa were achieved. The range of compressive strengths achieved indicated that the behavior of the bituminous binder during heat curing significantly influences the performance of the Bitublocks and suggested that bitumen hardening is highly influenced by the curing temperature. Oxidation as opposed to polymerization and loss of volatiles was confirmed to be the key role in the bitumen hardening process (only approximately 7% of the total long-term hardening was due to volatilization). The oxidation process can be directly linked to the compressive strength development of Bitublock.

The effects of fluctuating temperatures on the setting times of concrete mixtures made with different water-to-cement ratios, supplementary cementing materials (SCMs), and SCM dosages are evaluated in this paper. Initial and final set times of the concrete were determined with penetration resistance testing. Wet-sieved mortar samples were placed in hot and cold water baths that cycled over 24 h between temperature ranges of 32– $41°\text{C}$ and 4– $13°\text{C}$ , respectively. The control samples were cured at temperatures between 20 and $24°\text{C}$ . Results show that Class F fly ash will slightly retard setting, ground granulated blast furnace slag will slightly accelerate setting, and Class C fly ash will significantly increase setting times. It is shown that the equivalent age maturity method may be used to estimate setting times of concrete samples cured under fluctuating temperatures. Activation energy values are recommended for use with the equivalent age maturity method to predict setting.

The development of new binders, alternative to traditional cements mortars obtained by the reinforcement of some fibers and polymer emulsion, is an ongoing study and research topic of the scientific community. The present research investigates mechanical properties of cement mortar composites containing different hybrid combinations of polypropylene (PP) fibers and polymer emulsion. Effects of different PP fiber contents as partial replacement of mortar on the mechanical properties were evaluated, and effects of different polymer emulsion contents as partial replacement of mortar on the mechanical properties were also evaluated. In this article, a group of orthogonal test was arranged and proportioning design of PP fiber and polymer emulsion reinforced cement mortar was conducted. The experiment results showed that mixing 2.0% PP fiber and 9% polymer emulsion could enhance cement mortar’s mechanical properties to a certain degree. A mechanism of PP fiber and polymer emulsion enhancements was analyzed.

A new experimental apparatus was developed for determining the combined effects of mechanical stress and chemical exposure on the long-term durability of polymeric liners, which are widely used in civil and environmental engineering applications. The apparatus is capable of bending and holding up to 12 coupon-type specimens at predetermined levels of deflection while simultaneously exposing the specimens to a chemical solution bath. The apparatus was used to study the effects of three levels of deformation of 0.0, 0.03, and 0.08 mm/mm normalized deflection at the midspan of high-density polyethylene (HDPE) and low-density polyethylene (LDPE) specimens ( $3.2\times 12.7\times 63.5\text{mm}$ or $0.13\times 0.50\times 2.50\text{in}\text{.}$ ). The bent specimens were immersed in deionized water, chlorine (3 or 800 mg/L) or trichloroethylene (TCE) (3 or 1,000 mg/L) solution baths. The specimens were then stored at a constant temperature (23, 50, or $80°\text{C}/73$ , 122, or $176°\text{F}$ ) for a predetermined period of 1,250, 2,500, 3,750, and 5,000 h. Results of the tests indicate that neither TCE nor chlorine affect the modulus of elasticity of the tested HDPE and LDPE materials, whereas deformation at 8% normalized deflection (in deionized water and the chemical solutions) reduced the flexural modulus of elasticity of HDPE. In addition, elevated temperature $\left(80°\text{C}\right)$ combined with deformation had a notable effect on the ultimate strength of HDPE and elevated temperature only $\left(80°\text{C}\right)$ made all of the LDPE specimens fail.

Recycled aggregates may make an important contribution toward decreasing the adverse consequences of the production and the dumping of construction and demolition waste (CDW) on the environment. The results of the experimental research work carried out at Lisbon’s Instituto Superior Técnico and Laboratório Nacional de Engenharia Civil are presented in this article. Normalized laboratory tests to assess the performance of standard mortars were used to demonstrate the technical feasibility of recycling the waste produced by the ceramics industry and from the demolition of red-clay bricks or tiles to produce mortars with less/no consumption of natural aggregates. Results are very promising up to a replacement ratio of sand with ceramic waste of at least 20%. The paper presents useful data for the ceramics industry, builders and mortar manufacturing companies in terms of minimizing the impact of CDW and using eco-efficient materials.

Laboratory and field investigations were performed on several commercially available rigid polyurethane foam materials to determine their suitability as base replacement materials for full-depth portland concrete cement (PCC) pavement repairs. Rigid polyurethane foam (RPF) specimens were prepared and tested to evaluate the compressive strength, reactivity, and density of several foam materials under a variety of temperature conditions, where properties were investigated for thermal variations expected in field placement. Following laboratory testing, full-scale field testing of full-depth PCC repairs was conducted using two RPFs of densities of approximately $160\text{kg}/{\text{m}}^3$ $\left(10\text{lb}/{\text{ft}}^3\right)$ and $240\text{kg}/{\text{m}}^3$ $\left(15\text{lb}/{\text{ft}}^3\right)$ to verify laboratory predicted performance under elevated and ideal field temperatures. Each repair was trafficked within 3 h of repair completion with an F-15E load cart to simulate fighter aircraft traffic on early-age repairs. Results of laboratory and field testing indicate that high-density RPF materials are suitable as base replacement materials for temporary pavement repairs on airfields. For optimum field performance a RPF with minimum density of $240\text{kg}/{\text{m}}^3$ $\left(15\text{lb}/{\text{ft}}^3\right)$ should be placed at a temperature of $23°\text{C}$ $\left(70°\text{F}\right)$ .

This paper presents a study of the strength and carbonation resistance of mortar made with portland rice husk ash cement by some accelerated short-term techniques in 5% carbon dioxide. Three finenesses of rice husk ashes, viz., original rice husk ash (RAO), medium rice husk ash (RA1) with 15–20% by weight retained on a sieve No. 325, and fine rice husk ash (RA2) with 1–3% by weight retained on a sieve No. 325. Ordinary portland cement was partially replaced with RAO, RA1, and RA2. Compressive strength, porosity, and carbonation depth were determined. The result indicated that the RA2 decreased the water requirement to a lesser extent as compared to that of the RA1 and RAO. The use of RA2 produced mixes with good strength and low porosity of mortar. The carbonation depth increased with an increase in the replacement level for all rice husk ashes. The carbonation depth of RA2 was lower than those of RA1 and RAO. The carbonation depth increased with a decrease in compressive strength and with an increase in amount of water requirement.

Cementitious binders consisting of ground granulated iron slag and an alkaline activator (alkali activated slag) have considerable environmental benefits when used as an alternative to conventional 100% ordinary portland cement binders. The objective of this paper is to demonstrate the effect of pore cross section shape on unsaturated flow and to contrast the laboratory and numerical predictions of alkali activated slag binders and 100% portland cement binders. Convection-based uptake of water within capillary pores is modeled using pore size distribution data; however, most existing predictive models are based on the assumption of a circular cross section. This model allows for changeable capillary cross-sectional shape by employing ellipses ranging in shape from circular to slit. By applying a shape factor that accounts for departure from circularity of the pore cross section, the prediction model shows reasonable agreement with water sorptivity test data. As well as different binder types, the predictive model is assessed over a range of concrete ages and curing conditions.

Most of the techniques used today to evaluate practically moisture damage in asphalt pavements are involved in compacted asphalt mixtures. These tests generally simulate field conditions, and provide a performance-related parameter of moisture effects by applying mechanical techniques. No test of the compacted mixtures, however, can isolate the fundamental and rheological properties of the asphalt-aggregate bond, which hinder proper understanding and quantification of the moisture damage phenomenon. To avoid these complications and improve the evaluation of asphalt-aggregate interfacial properties in moist situations, this study proposes a new experimental method. In this method, dynamic shear rheometer was used to measure asphalt-aggregate interfacial properties. A degree of moisture damage relating to the interfacial properties was then quantified using linear viscoelastic concepts to propose a meaningful parameter, called wet to dry yield shear stress ratio. Moreover, possible factors such as film thicknesses, conditioning times, and chemical effects were studied in terms of the W/D YSS ratio.

The water-absorption behavior of cement pastes $\left(w/c=0.30\right)$ containing varying concentrations (i.e., 0, 0.2, and 5%) of a shrinkage-reducing admixture (SRA) was measured. Moisture ingress was monitored using X-ray absorption. A decrease in both the depth of water penetration and the rate of water absorption was observed with increasing specimen maturity and admixture concentration. This agrees with theoretical considerations that suggest water sorption is a function of the surface tension and the viscosity of the fluid ingressing into the pores. The Boltzmann-Matano method was successfully employed to determine the moisture content dependent moisture diffusivity of the material, which exhibited a dependence on both the pore structure (specimen maturity) and the SRA concentration.