Journal of Materials in Civil Engineering

The durability of unplasticized poly(vinyl chloride) (uPVC) components used in the building industry is a function of the interaction of several factors. Types and quantities of additives incorporated to the PVC resin and defining the formulation of the PVC compound used in the production of these components are among the most important such factors. White uPVC window profiles with different formulations have been exposed to five years of natural weathering under Brazilian climatic conditions. Results of Charpy impact tests were used to assess the influence of three factors on the durability of the profiles: additivation levels of titanium dioxide, nature of the impact modifier, and nature of the thermal stabilizer. Statistical analysis of the results made it possible to rank these factors according to their influence in component durability. The influence of composition of uPVC on mechanical properties of window profiles is demonstrated by means of the study of the modulus of elasticity. Results presented in this paper indicated the need for several additional experiments in order to check changes in molecular mass and color. Comparison of all these data with results from profiles subjected to accelerated weathering led to straightforward criteria for prediction of the potential behavior of uPVC, to be described in a future paper.

In predicting the chloride diffusivity of concrete as a three-phase material, the morphological characteristics of the three phases, the physical properties of each phase constituent material, and the interactions of the three phases in the concrete matrix should all be taken into account. The present paper attempts to develop an analytical method to achieve this. A three-phase composite sphere model for the concrete matrix is proposed to represent the heterogeneous nature of concrete and a closed form solution for the chloride diffusivity of concrete is derived. After verifying the derived closed form solution with experimental results, the effects of key factors that affect the chloride diffusivity of concrete, namely the chloride diffusivity and thickness of the interfacial transition zone (ITZ), the maximum aggregate diameter, and the aggregate gradation are examined in a quantitative manner. It is found in the paper that the most important factor influencing the chloride diffusivity of concrete is the chloride diffusivity of ITZ. When the aggregate volume fraction is equal to 0.8, the relative chloride diffusivity of concrete to cement paste for a given relative chloride diffusivity of ITZ to cement paste at 10 is almost four times that for a given relative chloride diffusivity of ITZ to cement paste at 2. The second most important factor is the thickness of ITZ. When the aggregate volume fraction is equal to 0.8, the relative chloride diffusivity of concrete to cement paste for a given ITZ thickness at $0.05\mathrm{mm}$ increases by 76% as compared to that for a given ITZ thickness at $0.02\mathrm{mm}$ . The least important factors are the maximum aggregate diameter and aggregate gradation. The extent to which they influence the chloride diffusivity of concrete is in the range of 10–55%. The paper concludes that the closed form solution derived here can predict the chloride diffusivity of concrete with reasonable accuracy.

In this experimental study an acoustic emission (AE) technique was used on geometrically similar notched plain concrete three-point bend specimens of different sizes. This study aims to measure the acoustic emission energy released during fracture process of plain concrete beams and to investigate the relation between acoustic emission energy to fracture energy of plain concrete beams of different sizes. The technique of acoustic emission uses one or more sensors to listen to a wide range of events that may take place inside a solid material. A series of concrete specimens of different sizes was tested for fracture energy. Acoustic emission energy release was monitored while testing concrete specimens for fracture energy. A correlation between fracture energy and acoustic emission energy was observed. Fracture energy was calculated from work of fracture. Size effect on the strength of concrete beams was observed. An equation has been proposed to obtain fracture energy by knowing acoustic emission energy.

Three different concentrations of crumb rubber were mixed with two different asphalts by means of a wet process to investigate the effect of rubber particles on the fundamental internal structure of asphalt binders with respect to their long-term aging performance. The rheological properties of unaged and aged unmodified and rubber-modified asphalt binders were studied as a function of long-term oxidative aging. Master curves were constructed by shifting the aging time-frequency data to assist in the interpretation. A generalized power-law model used in neat asphalt based on the time–temperature superposition principle was applied to construct the master curves of the rheological parameters. Based on a limited study, the results indicate that the amount of rubber particles added into the asphalt binder is asphalt dependent. The results also show that the stiffness effect of crumb rubber to one less-compatible asphalt is higher than the other highly compatible asphalt. Addition of crumb rubber to both asphalts reduced viscosity buildup with aging. In addition, rubber modification dramatically increased the elasticity of both asphalts. It is possible that rubber modification will improve rutting resistance because of the increased viscosity and elasticity at high temperatures and will improve fatigue resistance by either decreasing viscosity or lowering viscosity buildup with aging at low temperatures.

Rammed earth walls are formed by compacting subsoil in thin layers inside temporary supporting formwork. An ancient form of construction, rammed earth has in recent years, together with other earth building methods, been increasingly used structurally in a range of contemporary buildings in many countries around the world. Though current structural design procedures for earth walls, including rammed earth, in general use provisions based on structural masonry standards, this approach has never been satisfactorily validated. This paper presents experimental results from material and large-scale testing and develops a simple theoretical model, applied to rammed earth columns subject to concentric and eccentric axial compression loading. An analytical model, using a basic strut theory, shows favorable correlation with the experimental results for all load eccentricities.

The reactivity, or rate of consumption, of magnesium oxide $\left(\mathrm{MgO}\right)$ powder used in forming magnesium oxychloride (MOC) cement is largely affected by its thermal history and particle size. That, in turn, influences both reaction rate and properties of the reaction products of MOC cement. It is believed that the traditional measurements of properties of $\mathrm{MgO}$ powder itself are not able to reflect the actual consumption rate of $\mathrm{MgO}$ during chemical reaction, which is the key information needed for the appropriate proportions of starting materials to ensure the formation of Phase 5 crystals for better strength and physical properties. The experimental results show that X-ray diffractograms and phase diagram of a ternary MOC system can be utilized to evaluate the reactivity of $\mathrm{MgO}$ , and to optimize the formulation of MOC cement as well. Consequently, the apparent molar ratios of $\mathrm{MgO}$ over magnesium chloride $\left({\mathrm{MgCl}}_2\right)$ are adopted and recommended. The equivalent weight ratios between $\mathrm{MgO}$ and ${\mathrm{MgCl}}_2$ are also given for the convenience of normal applications.

This paper deals with the experimental characterization of the fracture surface of granite, obtained from direct tensile tests. The objective is to address the dependence of Mode I fracture energy on the fracture surface’s roughness, as well as to analyze the fracture propagation process based on the surface features. In addition, the influence of microstructural aspects on the fracture surface is also discussed. Different types of granites were studied, similar to the ones used in the fabric of ancient buildings, with distinct petrographical characteristics. The fracture surfaces were inspected with a novel 3D laser topographical inspection system aiming at acquiring the texture of fracture surface profiles at various locations on the surface. The relief of the fracture surfaces was characterized by means of classical parameters, namely, mean roughness and root-mean-square roughness. A deeper analysis was carried out by the separation of micro- and macroroughness regimes. This study reveals a clear linear trend between fracture energy and mean microroughness. Additionally, it was found that microstructural aspects, like planar anisotropy and grain size, as well as weathering state, influence the fracture surface. The results allow further understanding of the fracture process in quasi-brittle materials and contribute to the assessment of the mechanical characterization of granite under tension.

Good structural design demands high quality experimental data and reliable modeling of the mechanical properties of the constituent materials. Although several theoretical models and much experimental data on the behavior of fiber-reinforced concrete in compression are available in published literature, there are considerable reservations on the general applicability of these models for design. This paper presents the results of tests in compression of steel fiber-reinforced concrete carried out according to standard procedures, and a critical evaluation of the models proposed to define the stress-strain behavior in compression. The tests reported were carried out on cylindrical specimens of plain and steel fiber-reinforced concrete with fiber volume of 1, 1.6, and 3%. To evaluate the reliability of the models available in literature, a critical comparative study was carried out between the experimental data and the various proposed theoretical stress-strain relationships. It is shown that while many of the models showed good agreement with test results from which the model equations were derived, there was no such good agreement when the models were applied to other published test data.

This study relates value ranges of natural soil properties (plasticity, texture, and shrinkage) to the degree of predisposition of soils to stabilization for rammed earth wall construction. A total of 219 strength determinations were made on 104 soils compacted and stabilized with cement and/or lime and/or asphalt. Using a $2\mathrm{MPa}$ compressive strength criterion as the measure of stabilization success, soil property value ranges were related to the proportion of samples exceeding the criterion. Linear shrinkage (LS) and plasticity index (PI) are found to be the best discriminators of soil predisposition, with textural variables being useful secondary discriminators. “Favorable” soils, with stabilization success rates of $\ge 80\%$ , include those with: (1) $\mathrm{LS}<6.0\%$ and $\mathrm{PI}<15\%$ ; and (2) LS 6.0–11.0%, PI 15–30%, and sand content $<64\%$ . These soils were stabilized with treatments averaging 4.2% cement and 1.8% lime, with individual treatments ranging from 4–8% total cement and/or lime. “Unfavorable” soils, with stabilization success rates of $<60\%$ , include those with LS 6.0–11.0, PI 15–30, and sand content $\ge 64\%$ , or with $\mathrm{LS}>11.0$ , $\mathrm{PI}>30$ . These findings should assist rammed earth engineers to more easily select a suitable soil and to minimize resources spent on preconstruction stabilization trials.