Journal of Materials in Civil Engineering

Glass fiber-reinforced concrete (GRC) is a material made of a cementitious matrix composed of cement, sand, water, and admixtures, in which short-length glass fibers are dispersed. It has been widely used in the construction industry for nonstructural elements, especially façade panels. Based on the recent results of a research project, this material was applied to the fabrication of structural elements, namely, 30-m-high telecommunication towers and pedestrian bridges. In these structures, the effects of cyclic loads, like wind, earthquakes, or pedestrian circulation, are important, and the corresponding GRC behavior has to be considered in their structural design. This paper focuses on the experimental evaluation and numerical modeling of GRC mechanical behavior. Based on the results of experimental tests on material samples, a numerical model was developed to reproduce the cyclic and monotonic behavior of GRC. This numerical model was then used to assess the structural behavior of GRC telecommunication towers.

This paper discusses the superelastic behavior of shape memory alloy, Nitinol $\left(\mathrm{NiTi}\right)$ , when used as reinforcement in concrete beams. The ability of $\mathrm{NiTi}$ to recover and reduce permanent deformations of concrete beams was investigated. Small-scale concrete beams, with $\mathrm{NiTi}$ reinforcement were tested under half-cycle loads. The reinforcement ratio varied from 0.1 to about 0.9%. The experimental results showed that the average residual displacement in the $\mathrm{NiTi}$ reinforced beams was less than one-fifth of that of the steel reinforced test beams. The stiffness of $\mathrm{NiTi}$ reinforced test beams however was lower than those of the steel reinforced test beams. An analytical study of load–deflection relationship for a series of hybrid beams was undertaken. It was found that a hybrid system that incorporated $\mathrm{NiTi}$ combined with high strength steel or carbon fiber reinforced plastic bars was a better choice for design because of their relatively high stiffness.

Strength and durability are two key factors influencing the safety and service life of fire-damaged concrete structures. To develop an assessment method for fire-damaged high-strength concrete (HSC) structures that is convenient for postfire repair, the effects of concrete strength and aggregate type on the postfire residual compressive strength of HSC were studied in this paper. Subsequently, the changes in durability and microstructures were investigated by the rapid chloride-ion penetrability test, the mercury intrusion porosimetry test, and scanning electron microscopy observation, respectively. Based on the test results and further analysis, estimation of the temperature distribution in the fire-damaged concrete element is established by the dichotomy and mercury intrusion porosimetry test and scanning electron microscopy observation. According to the estimated temperature distribution, the postfire residual compressive strength can be assessed by the strip method and postfire durability can be assessed by the “two-level” method, respectively. Based on the assessments, the repair method for fire-damaged HSC structures is recommended in steps.

Slag was utilized as an additive for fly ash-based geopolymers in this study. It was found that the incorporation of slag could significantly increase the compressive strength of the geopolymer. The compressive strength of geopolymer with 4.0% slag reached 50 and $70\mathrm{MPa}$ when cured for $14\text{days}$ at 30 and $70°\mathrm{C}$ , respectively. The mechanism of slag as additive on the enhancement of compressive strength of geopolymer was investigated using X-ray diffractometer (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and mercury intrusion porosimetry (MIP). The XRD and FTIR results showed that the addition of slag could generate more amorphous products and accelerate the reaction rate of raw materials. From XPS results, the decrease of binding energy and a broadening of peaks were observed for $\mathrm{Si}2p$ , $\mathrm{Al}2p$ , and $\mathrm{O}1s$ elements due to the ${\mathrm{Ca}}^{2+}$ provided by slag. The decrease in binding energy was more favorable to zeolite formation. The results of MIP suggested that the 4% slag addition significantly influenced pore structure of geopolymer. A refinement of pore size was exhibited after 4% slag addition, especially for specimens being cured at $70°\mathrm{C}$ . For these reasons, the compressive strength of geopolymer made with 4% slag addition was greatly improved.

Improved understanding of rutting resistance of a rubberized asphalt concrete pavement that contains reclaimed asphalt pavement (RAP) is important to stimulating the use of rubberized asphalt mixtures. Use of RAP in the past has proved to be economical, environmentally sound, and effective in increasing the rutting resistance of asphalt mixtures. Rubberized asphalt has been used successfully in improving the mechanical characteristics, such as rutting resistance, of typical hot mix asphalt (HMA) mixture around the country and the world. The objective of this research was to investigate the rutting resistance characteristics of the rubberized asphalt mixtures through a laboratory testing program. The experimental design included use of two rubber types (ambient and cryogenically produced), four rubber contents, and three crumb rubber sizes. The results of the experiments indicated that the use of RAP and crumb rubber in the HMA can effectively improve the rut resistance of these mixes.

Experiences show that the design of overlay mortars is a complicated matter as far as long-term durability and dimensional stability are concerned. In many cases, applied mortars crack or delaminate a few years after application. The same is true for passive fire protection mortars (PFP mortars). The mortar must remain crack free and must not delaminate during the planned service life, that means the fire protection requirements must be combined with the durability requirements. In this paper, an approach based on a numerical model is used to forecast the long-term behavior of PFP mortars. By means of this model, the time-dependent humidity, temperature, stress, and strain distributions, as well as the crack formation can be calculated in a realistic way. The minimal adhesive strength between overlay and substrate which is necessary to prevent delamination during the planned service life has been calculated. Material properties and climatic boundary conditions have been taken into account. The results allow the tailored optimization of PFP mortars.

In order to evaluate material characteristics (in situ modulus) of well-compacted subgrades, the portable falling weight deflectometer (PFWD) test, which simulates dynamic loads, was adopted. The falling energy was assumed as a dynamic load and a well-compacted subgrade was treated as an ideal elastic body. In addition, the static plate-bearing load test (PBLT) was used to evaluate the coefficient of subgrade reaction. The PFWD test and PBLT for a total of 22 testing points were carried out on well-compacted subgrades at two different highway construction sites (A and B). Three falling heights and weights were used to produce six different levels of dynamic loads. The test results show that there is a reasonable linear correlation between the dynamic deflection modulus and the coefficient of subgrade reaction of well-compacted subgrades. It was also found that the dynamic deflection modulus is not largely affected by variation of the falling energies. Application of the PFWD for compaction control and as an alternative method to the PBLT would lead to significant cost savings.

This paper deals with the viability of using reclaimed polyethylene (PE) derived from low-density PE carry bags collected from domestic waste as an additive in asphalt concrete mixtures. Different ratios of PE (2.5, 5.0, 7.5, and 10% by weight of asphalt) were blended with (80/100)-paving grade asphalt. The dynamic creep test (unconfined), indirect tensile test, resilient modulus test, and Hamburg wheel track tests were carried out on asphalt concrete mixtures blended with PE. The analyses of test results show that the performance of PE-modified asphalt mixtures are better when compared to conventional mixtures. The rutting potential and temperature susceptibility can be reduced by the inclusion of PE in the asphalt mixture. A PE content of 5% by weight of asphalt is recommended for the improvement of the performance of asphalt concrete mixtures similar to that investigated in this study.

The viscoelastic behavior of asphalt mixtures can be conveniently presented in the form of a stiffness master curve in various engineering applications. However, the methods to obtain the in-service mixture stiffness are limited to the falling weight deflectometer (FWD) testing and back-calculation procedure because the pavement layer thicknesses in many cases are too thin to allow laboratory testing. The test protocol to measure the axial dynamic modulus requires cylindrical specimens with a height-to-diameter ratio higher than 2, while the cores need to be at least $38\mathrm{mm}$ thick for measuring shear stiffness. This technical note describes and compares the methods for constructing asphalt mixture master curves utilizing stiffness predictive equations for asphalt binders and mixtures, in addition to using laboratory measurements, as an alternative to FWD backcalculation analysis. This technical note also recommends constraining the low and high mixture stiffness values measured from simple shear testing to obtain stiffness comparable to the uniaxial dynamic modulus testing.

The recycling of reclaimed asphalt pavement (RAP) is typically achieved by adding a rejuvenating agent into the mix. The addition of the rejuvenating agent leads to adjusting the compositions and consequently improving the physical and performance properties of the rejuvenated aged binders in the RAP. Many rubberized pavements, around the country, are over $15\text{years}$ old and some of them are a candidate for recycling. Therefore, there is a need to study the effects of rejuvenating agents on aged crumb rubber modified binders (CRM binders). This paper presents a study characterizing the blends of laboratory-aged CRM binders and rejuvenating agents using gel permeation chromatography (GPC), resulting in the development of empirical models to predict selected properties of the blends. Three aged CRM binders and two aged control binders (PG 76-22) were mixed with either a rejuvenator or a softer binder at different concentrations to determine the influence of the various asphalt binders and the rejuvenating agents on the chromatographic profiles. The results indicated the compositional changes of the blends containing various percentages of either the rejuvenator or the softer binder are well reflected by the GPC profiles. The large molecular size (LMS) of the blends decreased and the small molecular size (SMS) increased as the percentage of the rejuvenator agents increased regardless of the type of aged binders or the rejuvenating agents. The empirical prediction models for Superpave binder properties (viscosity and high-failure temperature) were developed using LMS and SMS. The predicted values showed a high correlation with the viscosity and the high-failure temperature of binders.

A series of four-point bending, quasi-static and high-cycle fatigue tests has been conducted on aluconcrete beams consisting of an aluminum extrusion acting compositely with a high-strength concrete infill. Observations and analysis of the quasi-static tests and test results indicate that fully effective composite action was maintained up to failure, with negligible or minimal slip occurring between the aluminum extrusion and high-strength concrete. Failure of the beams during the high-cycle fatigue tests resulted from a gradual degradation of the bond between the concrete and aluminum, resulting in noticeable slip and a corresponding reduction in composite action. Even so, the fatigue test beams, which had a shear bond transmission length of only $575\mathrm{mm}$ , were able to sustain approximately one-quarter of a million load cycles from approximately 5 to 50% of their ultimate load.