Journal of Materials in Civil Engineering

The use of high percentages of recycled aggregates in concrete would usually worsen the concrete properties. This paper tries to address the deficiency of the use of recycled aggregates by systematically presenting results on the influence of incorporating Class F fly ash on concrete properties. In this study, two series of concrete mixtures were prepared with water-to-binder (W/B) ratios of 0.45 and 0.55. The recycled aggregate was used as 0, 20, 50, and 100% by weight replacements of natural aggregate. In addition, fly ash was used as 0, 25, and 35% by weight replacements of cement. The results showed that the compressive strengths, tensile strengths, and static modulus of elasticity values of the concrete at all ages decreased as the recycled aggregate and the fly ash contents increased. Further, an increase in the recycled aggregate content decreased the resistance to chloride ion penetration and increased the drying shrinkage and creep of concrete. Nevertheless, the use of fly ash as a substitute for cement improved the resistance to chloride ion penetration and decreased the drying shrinkage and creep of the recycled aggregate concrete. The results showed that one of the practical ways to utilize a high percentage of recycled aggregate in structural concrete is by incorporating 25–35% of fly ash as some of the drawbacks induced by the use of recycled aggregates in concrete could be minimized.

Fabric reinforced cement based composites are a new class of composites with superior tensile strength and ductility which have the potential for becoming load bearing structural members. This enhanced behavior is primarily governed by interfacial bond characteristics between fabrics and matrix. Pullout tests were conducted using several different matrices and fabric types: two different mix designs (control and with fly ash); and four fabric types: alkali-resistant glass, polypropylene, polyethylene, and polyvinyl alcohol. The effects of processing methods: cast, pultrusion, and vacuum as well as fabric embedded lengths (7.6 and $12.7\mathrm{mm}$ ) were also evaluated. The Naamam 1991 pullout model was modified in this paper and used to investigate the bond mechanism expressed as shear strength diagram. The shear strength parameters obtained by fitting the pullout simulation curves to the experimental responses are agreed well with the nominal shear strength obtained directly from the experiments. It was found that the pullout responses are highly dependent on the fabric type, mixture design, and processing method.

The uniaxial monotonic compressive stress-strain behavior and other characteristics of unreinforced masonry and its constituents, i.e., solid clay bricks and mortar, have been studied by several laboratory tests. Based on the results and observations of the comprehensive experimental study, nonlinear stress-strain curves have been obtained for bricks, mortar, and masonry and six “control points” have been identified on the stress-strain curves of masonry, which can also be used to define the performance limit states of the masonry material or member. Using linear regression analysis, a simple analytical model has been proposed for obtaining the stress-strain curves for masonry that can be used in the analysis and design procedures. The model requires only the compressive strengths of bricks and mortar as input data, which can be easily obtained experimentally and also are generally available in codes. Simple relationships have been identified for obtaining the modulus of elasticity of bricks, mortar, and masonry from their corresponding compressive strengths. It was observed that for the strong and stiff bricks and mortar of lesser but comparable strength and stiffness, the stress-strain curves of masonry do not necessarily fall in between those of bricks and mortar.

Different methods for preliminary constituent proportioning of the recycled mix are proposed in various guidelines/studies for central plant hotmix asphalt recycling. These methods are sequential in nature, and the process requires at least one of the parameters (for example, quantity of reclaimed material or viscosity of virgin asphalt binder) as fixed. An attempt has been made in the present work to develop a generalized formulation for the mix proportioning which does not require any such prefixing; however, the formulation is flexible enough to take care of such a constraint, if imposed. The proposed formulation serves certain overall objectives, like minimization of material cost, maximization of usage of reclaimed material etc., with the help of a linear programming tool. The suggested approach handles the proportioning problem as a whole, and is therefore not dependent on the sequence of mix proportion calculations.

Fatigue damage is a distress observed in asphalt pavement at moderate to low temperatures due to cyclic loading of moving traffic. Recent developments in binder fatigue research have been made using parallel plate geometry in a dynamic shear rheometer (DSR) to measure total dissipated energy and its change as a function of test cycles. Recent studies, however, have raised questions regarding the temperature level and stiffness level at which true binder fatigue can be measured with the parallel plate geometry in the DSR. It has been claimed that the binder’s stiffness of less than $15\mathrm{MPa}$ will result in instability failure known as “edge effect,” instead of true fatigue. Edge effect, better known as edge fracture in polymer science, is a normal-force dependent phenomenon which is characterized by the inability of material to maintain its geometry at its boundary with air/atmosphere. This study attempts to investigate further the relationship between binder’s stiffness and true fatigue using parallel plate (PP) geometry and torsion cylinder (TC) geometry. TC samples are a cylindrical-shaped mix of asphalt binder and Ottawa sand (one size, pass No. 30 sieve, and retained on No. 50 sieve), $12\mathrm{mm}$ in diameter and $30\mathrm{mm}$ in height, produced using metal molds, to simulate the effect of traffic load on thin asphalt film in asphalt mixtures. Torsion cylinder high stiffness (range) ensures that the sample will fail in true fatigue. This study hypothesized that PP and TC test results are related, and should PP and TC behave in a similar way, edge effect can be considered not significant enough to effect parallel plate fatigue testing. Testing was done by three different laboratories to evaluate repeatability between these two geometries. A simple shift parameter based on testing geometries allows direct comparison between PP and TC test results. Binder stiffness role in similarities and differences in both geometries is presented. Regression analysis using Minitab showed that test geometry was not sufficiently significant to affect fatigue test results, thus the edge effect was not significant in PP fatigue testing. The same analysis indicated that repeatability is significant in the PP regression model, but not in the TC regression model. This indicated that TC has better repeatability than PP, and showed that sample preparation and adhering of asphalt film to parallel plates can be dealt with by using torsion cylinder geometry.

The spherical indentation response of a dense bitumen macadam asphalt mixture with two different volume fractions of bitumen binder is investigated both experimentally and via an analytical model. The model for the indentation of bitumen developed by Ossa et al. in 2005, was used to study the spherical indentation behavior of the mixtures with good agreement when compared to experimental results. An extensive experimental study of the monotonic and recovery spherical indentation behavior is reported for a range of temperatures. In line with the predictions of the model, the monotonic indentation response of the mixtures exhibits a power-law dependence on the indentation force. The model is also successful in capturing the indentation recovery behavior of the mixtures. A comparison of the material parameters obtained from uniaxial compression and indentation tests showed that indentation tests can be used in an easy and reliable way to obtain the fundamental asphalt parameters. Further, parameters found from indentation tests implicitly account for the confining conditions generated by the aggregate particles below the indenter.

Two metakaolins, with similar mineralogical composition but which vary in their surface area (11.1 versus $25.4{\mathrm{m}}^2∕\mathrm{g}$ ), were evaluated for use as supplementary cementitious materials through measurements of workability, setting time, strength, elastic modulus, heat evolution, calcium hydroxide (CH) content, and surface area. Compressive and flexural strength of concrete were greater and increased at a faster rate when the finer metakaolin was used, as expected. The addition of metakaolin increased early age (i.e., $1–3\text{days}$ ) flexural strength by as much as 60%. The effect of metakaolin surface area on compressive strength was particularly evident at the lower water-to-cementitious materials ratios (w/cms) examined and generally at later ages (i.e., $7\text{days}$ or later). However, although greater in the metakaolin–cement concretes than the ordinary concretes (particularly at the lowest w/cm examined, 0.40) elastic modulus measured at $28\text{days}$ , was not affected by the metakaolin surface area. The greater surface area metakaolin caused a greater and more rapid heat evolution, indicating a higher reactivity and a greater rate of hydration product formation. Both metakaolins decreased CH content compared to controls, with the consumption of CH extending beyond $14\text{days}$ . Surface area measurements indicated a more refined pore structure relative to controls by $28\text{days}$ . These analyses illustrate the effect of metakaolin fineness on pozzolanic reactivity, associated CH consumption, and pore structure refinement, and suggest links to the observed increased mechanical properties of metakaolin–concretes.

A series of triaxial compression tests and cyclic triaxial tests were conducted on unreinforced and geogrid reinforced crushed limestone samples to investigate the effects of the geogrid type, location, and number of layers on the strength, stiffness, and cyclic deformability of these samples. Five different types of geogrids were used. For each geogrid type, four different reinforcement arrangements were investigated. Comprehensive statistical analyses were conducted on the collected triaxial test data. The results of these analyses indicated that the geogrid inclusion within crushed limestone samples increased significantly their elastic modulus and ultimate shear strength, while it reduced their permanent deformation; thus, the geogrid is expected to enhance the performance of base course material in the field and reduce its deformation. The results also showed that stiffer geogrids exhibited greater improvement. Moreover, samples reinforced with two geogrid layers placed at the upper and lower third of the sample height always had the highest improvement, while the lowest improvement was observed for samples with a single geogrid layer placed at the sample’s midheight. Finally, the results demonstrated that the geogrid did not have a significant effect on the resilient behavior of the crushed limestone samples.

In view of the importance of percolation of the interfacial transition zones (ITZs) in concrete to its transport properties, it is necessary to determine the ITZ percolation threshold for any aggregate gradation and ITZ thickness. This paper presents a numerical method for predicting the ITZ percolation threshold of concrete. To represent the mesostructure of concrete as realistically as possible, a simulation algorithm for the distribution of aggregate particles and ITZs in concrete with periodic boundary conditions is proposed. By analyzing and studying the numerical results, it is shown in this paper that, for a given aggregate volume fraction and element size, the ITZ percolation probability tends to be a constant for a sufficient number of simulations and that the slope of the ITZ percolation probability curve becomes vertical as the element size increases. Finally the results produced by the proposed numerical method are verified by experimental results obtained from the research literature. Based on the results presented in this paper, the effects of the ITZ thickness, the maximum aggregate diameter, and the aggregate gradation on the ITZ percolation threshold are evaluated in a quantitative manner. It can be concluded that the numerical method developed can be used to predict the ITZ percolation threshold with reasonable accuracy.

Nondestructive testing techniques are increasingly being used to obtain the geometry of structural and nonstructural elements and hidden features such as voids, cracks, and detachments. However, the evaluation of the compressive strength and other mechanical properties of ancient materials using such techniques remains a challenge. To reliably assess mechanical properties, it is usually necessary to directly test the strength and deformation of materials by destructive methods. To avoid coring and sampling of the historic fabric, a recent minor-destructive methodology based in microdrilling is used in this paper for the characterization of clay brick. For this purpose, 148 brick specimens from the 12th to 19th centuries were collected from six monasteries in Portugal. A wide range of compressive strength was found by destructive compressive testing, ranging from $6.7\text{to}21.8\mathrm{N}∕{\mathrm{mm}}^2$ . The paper shows that it is possible to reliably estimate the compressive strength of bricks by means of regression curves using the adopted microdrilling technique.