Journal of Materials in Civil Engineering

This paper investigates the effects of the fineness and replacement ratio of fly ash on the temperature rise and setting time, and compressive, tensile, and flexural strength of mortar mixtures. Three types of fly ash with Blaine finenesses of $4,125{\mathrm{cm}}^2/\mathrm{g}$ (40F), $6,686{\mathrm{cm}}^2/\mathrm{g}$ (60F), and $9,632{\mathrm{cm}}^2/\mathrm{g}$ (90F) were used to replace Portland cement at replacement ratios of 0 (which was the control mix), 15, 30, 45, and 60% by binder mass. Test results demonstrate that using fly ash as a cement replacement resulted in a reduction in the maximum temperature rise in mortar regardless of the fineness of the fly ash. In this investigation, 15 fly ash replacement caused a reduction in the peak temperature of about 4 to 6°C in the mortar. The setting time of fly ash mixes where 15 and 30% of the cement was replaced with fine fly ashes was faster than that of the control mix. The compressive strength of mortar mixes using finer fly ashes (60F and 90F) was significantly improved compared to that of the 40F fly ash mortar.

A two-dimensional non-linear finite-element analysis micro-modeling approach to simulate unreinforced masonry beams in bending is extended to include a retrofit with a thin layer of ductile fiber-reinforced cement-based material referred to as engineered cementitious composite (ECC). The retrofit method is one that has been demonstrated to add significant ductility to unreinforced masonry infill walls under in-plane cyclic loading and is further expected to enhance out-of-plane bending resistance. The objective of the research is to identify and propose a modeling approach for this complex system of four materials and three different types of interface using basic material properties and established model parameters for future analyses of the retrofit system in structural applications. Of the two geometric models investigated, a simplified approach using expanded brick units with zero-thickness mortar elements is recommended and validated. Brick-mortar interface opening, cracking of the ECC layer below the mortar joints, and failure of the ECC were captured well. The simulated response is found to be particularly sensitive to the adopted constitutive model of the ECC. Research areas for enhancing the ability of the adopted modeling approaches in predicting the response of this complex system, are identified.

The thermal propagation through tensile cracks in reinforced concrete beams is examined experimentally. A comparison is made between the rate of thermal propagation through beams that are undamaged, beams that have minor cracking, and beams that have major cracking. The results show a small decrease in the thermal propagation of the cracked beams in comparison with undamaged beams during heating. It is determined that the differences observed are most likely attributable to small geometric, mechanical, and concrete compositional differences. Consequently, it is concluded that the effects of tensile cracking on the thermal propagation through concrete can be ignored in structural analyses. Significantly, this means that analyses of heated concrete structures that are cracked can be carried out with heat-transfer and mechanical analyses being conducted sequentially, as is currently normal, and fully coupled thermomechanical analyses are not required.

This paper presents the results of studies conducted with neural networks on determining the properties of polymer concrete with fly ash. Polymer concrete with different contents of fly ash and resin was prepared and tested for determining the influence of fly ash on the properties. Using neural networks, the experimental results were analyzed for predicting the compressive strength and flexural strength, and also on the basis of a model with given values of properties, to ascertain the composition (content of resin, aggregate, and fly ash). Eleven sets were considered for training and four for verification. Reverse modeling proves that the largest values for compressive strength and flexural strength are obtained for a resin content of approximately 15–16%, and a fly ash content of approximately 8–9%.

Mix proportions of $n$ aggregate groups to form a combined aggregate batch for each one of 28 target curves of gradations from very stony to very sandy, all within and parallel to the granulometric bound curves of the German Standard: DIN-1045, are computed by three different approaches. The sum of the ratios of $n$ aggregate groups must equal 1 by any method. For any one of $m$ standard sieves, the sum of percent passings of $n$ groups multiplied by their ratios must equal the percent passing of a target curve, which is a linear equation, and $m$ linear equations result for $m$ sieves. Therefore, along with the first equation, the first approach composes the rest ($n-1$) number of linear equations out of any ($n-1$) number of $m$ standard sieves. In the second approach, a quasi-least-squares algorithm is used to minimize the sum of squares of differences of percent passings of the combined aggregate batch from those of a target curve for all sieves. In the third approach, the artificial bee colony (ABC) algorithm is used to minimize the sum of the absolute differences of the percent passings of the combined aggregate batch from those of a target curve for all sieves. The three approaches give mostly close solutions for many cases.

When cracks occur in concrete, released fracture energy will be proportionally transformed into the energy contained in acoustic emission (AE). According to this physical phenomenon, AE technology provides an effective monitoring method for fracture process of concrete through acquiring generated AE. However, such monitoring is limited in qualitative evaluation of fracture process under most occasions. Quantitative interpretation of fracture process is difficult to accomplish by simply acquiring the amount of AE generated or conducting parameter-based AE analysis. This paper investigates the feasibility of reflecting the fracture energy released during fracture by means of evaluating the energy index of detected AE signals. An effective fracture model based on fracture behavior of concrete cylinder under uniaxial compression is introduced here to provide a mathematical relationship between acquired AE energy index and crack formation energy of concrete. Apart from reasonably estimating the energy consumed for crack formation, cement-based piezoelectric sensors are embedded inside the concrete to carry the task of detecting AE and transforming its energy into the electrical energy of AE signals. On the basis of experimental study, the energy of detected AE signal is satisfactorily correlated to the corresponding fracture energy and quantitatively represents the fracture energy releasing process of concrete during the period of stable cracks development.

In this paper, the relationship between concrete damage and air flow is evaluated using model-scale reinforced concrete walls. The focus is on the walls behavior under uniaxial and biaxial loading conditions. The method for evaluating the damage-flow rate relationship includes structural testing of scaled specimens, damage identification, and air flow rate experiments. Concrete damage is characterized on a local and global level, via consideration of crack characteristics (length and width) and drift ratio, respectively. Nine model uniaxial specimens and 13 model biaxial specimens were tested, with variations in geometry, material, and loading details. All specimens had a well-defined region of interest for damage identification and air flow testing. Air flow tests, in the form of pressure decay tests, were used to measure the permeability of the concrete at different loading stages. Results indicate that the largest cracked concrete permeability occurs in specimens with low concrete strength, low reinforcement ratio, higher cycle count loading protocols, low axial load, and low aspect ratio. In contrast, the lowest cracked concrete permeability values are associated with high strength concrete, high reinforcement ratio, and high axial load.

The increased permeability that develops in damaged concrete walls translates directly to increased leakage of gases through the wall. For reinforced concrete structures housing dangerous gases, it is important to evaluate the level of containment the structure is providing subsequent to development of damage; therefore, knowledge of the leakage rate through the wall is of upmost importance. Using results from an experimental program described in a companion paper, the leakage of air through damaged reinforced concrete wall specimens subjected to both uniaxial and biaxial loading conditions is assessed. Results suggest applicable leakage rate formulas and highlight limitations when using such formulas for future predictive analyses.

The present paper deals with the energy dissipation induced by the viscous behavior of bituminous materials constituting pavement. An approach to take into account viscous properties of bituminous layers and to quantify this dissipation is explained. First, the behavior of different bituminous materials is investigated. Linear viscoelastic modeling is then proposed using a rheological model previously developed at the Civil Engineering and Buildings Department (DGCB) of the University of Lyon / ENTPE (Ecole Nationale des Travaux Publics de l’Etat). Second, this model is implemented in a finite-element code, which enables simulation of the behavior of any pavement structures under any rolling load. In this paper, these developments, previously validated for orthotropic steel bridge and mix surfacing structures, are applied on a classical French pavement structure. In addition, the calculation of energy dissipation due to the viscous properties of the bituminous materials is allowed. Then an estimation of corresponding fuel consumption excess is given considering a 40-ton truck for different temperatures and speeds. The influence of the base course thickness is investigated as well. The simulation results show that energy dissipation in bituminous pavement due to the rolling weight of the considered 40-ton truck may induce a fuel consumption excess of a few percents age points in very unfavorable climatic conditions.

Reuse of construction and demolition waste (CDW) as a road base material is one of the effective methods to reduce environmental effects caused by CDW dumping in landfills. To explore the feasibility to reuse CDW as a cement-treated material, this paper investigated the compressive and indirect tensile strengths of cement-treated demolition waste. Because the recycled CDW is a mix of recycled masonry and concrete, different ratios of recycled crushed masonry-concrete aggregates by mass were chosen in this study. Four mixture variables (cement content, degree of compaction, masonry content, and curing time) and their influence on the mechanical properties of cement-treated mix granulates (${\mathrm{CTM}}_i{\mathrm{G}}_r$) were then considered. Experimental results showed that a general model to estimate the compressive and indirect tensile strengths of ${\mathrm{CTM}}_i{\mathrm{G}}_r$ can be established in relation to those four mixture variables. Compared with normal cement-treated granular materials, the masonry content is another unique factor to determine the mechanical properties of ${\mathrm{CTM}}_i{\mathrm{G}}_r$ and its failure pattern. Furthermore, this study showed that ${\mathrm{CTM}}_i{\mathrm{G}}_r$ may be designed to have a good mechanical strength as a cemented road base.

The formation process of magnesium potassium phosphate hexahydrate was studied by monitoring the pH development of the $\mathrm{MgO}\mathrm{\text{-}}{\mathrm{KH}}_2{\mathrm{PO}}_4\mathrm{\text{-}}{\mathrm{H}}_2\mathrm{O}$ system. It is found that a typical potentiometric curve goes through several rises and drops, forming two local peaks and two local valleys, before reaching a plateau at pH of approximately 10.5. The characteristic points of the curve are identified and then utilized to distinguish the different reaction stages during the formation of the hexahydrate. By comparing the potentiometric curves of the ternary systems with different molar ratios, and from X-ray diffractometry analysis of the precipitates extracted at different stages, the formation of the hexahydrate most likely proceeds stepwise through two crystalline intermediates, namely $\mathrm{MgHP}{\mathrm{O}}_4·7{\mathrm{H}}_2\mathrm{O}$ and $\mathrm{M}{\mathrm{g}}_2\mathrm{KH}(\mathrm{P}{\mathrm{O}}_4{)}_2·15{\mathrm{H}}_2\mathrm{O}$. The thermal behavior of the formation process of magnesium potassium phosphate hexahydrate, including the formation and transformation among the intermediates and final product, is further verified by thermodynamic calculation. Finally, the morphologies of the different crystalline phases of the ternary system are examined by a scanning electron microscope (SEM).

When exposed to elevated temperatures, various constituents in hardened cement paste will undergo decomposition, resulting in thermal damage of concrete. To better understand the thermal damage mechanism, it is essential to investigate the whole decomposition process of hardened cement paste. Based on the kinetic and stoichiometric analysis, a numerical method is presented in this paper for predicting the thermal decomposition of hardened cement paste. In this method, the initial volume fractions of various constituents in hardened cement paste are expressed as a function of the water-to-cement ratio, degree of hydration, and the chemical composition of cement. By analyzing the kinetics of decomposition, the volume fraction evolution of each constituent is then formulated in terms of the heating rate and temperature. When silica fume is added, the pozzolanic reaction is also considered. Finally, the validity of the proposed numerical method is verified with three sets of experimental data collected from the literature. The effect of the heating rate on the thermal decomposition of hardened cement paste is evaluated in a quantitative manner.

The use of titanium dioxide (${\mathrm{TiO}}_2$) coating for pavements has received considerable attention in recent years to improve air quality near large metropolitan areas. However, the proper method of applying TiO2 to asphalt pavements is still unclear. This study evaluated the benefits of incorporating ${\mathrm{TiO}}_2$ in the preparation of warm-mix asphalt (WMA). Two application methods to integrate ${\mathrm{TiO}}_2$ were evaluated, a water-based ${\mathrm{TiO}}_2$ solution applied as a thin coating and using ${\mathrm{TiO}}_2$ as a modifier to asphalt binder in the preparation of WMA. On the basis of the results of the experimental program, it was determined that the photocatalytic compound was not effective in degrading ${\mathrm{NO}}_{\mathrm{x}}$ in the air stream when used as a modifier to the binder in the preparation of WMA. This could be attributed to the fact that only a small amount of ${\mathrm{TiO}}_2$ is present at the surface. When used as part of a surface spray coating, ${\mathrm{TiO}}_2$ was effective in removing nitrogen oxide (${\mathrm{NO}}_{\mathrm{x}-}$) pollutants from the air stream with an efficiency ranging from 31 to 55%. The maximum ${\mathrm{NO}}_{\mathrm{x}}$ removal efficiency was achieved at a coverage rate of $0.05\mathrm{L}/{\mathrm{m}}^2$. However, durability of the surface spray coating requires further evaluation. In addition, the increase in flow rate and relative humidity negatively impacted the effectiveness of ${\mathrm{NO}}_{\mathrm{x}}$ reduction efficiency. In contrast, the increase in ultraviolet (UV) light intensity improved the ${\mathrm{NO}}_{\mathrm{x}}$ removal efficiency of the surface coating.

This paper presents the measurement of rapid chloride ion permeability (charge passed) values through carbonated and non carbonated ordinary portland cement (OPC)– and portland pozzolana cement (PPC)-based concretes. When concrete is carbonated, the pores in it are filled by the carbonation products, resulting in lower porosity and permeability and substantially increased compressive strength and giving an impression that concrete is impervious. Hence, an assessment of the influence of carbonation on rapid chloride ion permeability becomes essential. Experimental investigation on carbonation was carried out on three different grades of concretes [water-to-cement ($\mathrm{w}/\mathrm{c}$) ratio of 0.40, 0.45, and 0.55], with four curing periods (28, 56, 90, and 120 days), and each for two types of commercially available cement, OPC and PPC. The specimens were kept in an accelerated carbonation chamber for 150 days with 10% carbon dioxide (${\mathrm{CO}}_2$), and then rapid chloride ion permeability through these carbonated specimens was measured with a rapid chloride ion permeability apparatus. The results indicate that a significant decrease in charge passed through concrete owing to carbonation can lead to misleading results in evaluation of the service life of the concrete structures. It is also observed that a low-$\mathrm{w}/\mathrm{c}$ concrete with PPC has discernible resistance to carbonation and rapid chloride ion permeability compared with its counterpart OPC.

The ultra-high strength concrete (UHSC) used in this study had a compressive strength greater than 145 MPa and was produced using materials commonly available in southern New Mexico. Specifically, locally available Type I/II cement, local sand with a top size of 600 μm, silica fume, steel fibers (13 mm long), and high-range water reducing admixture were used to produce the UHSC mixture with a water-to-cementitious materials ratio of 0.20. UHSC specimens were heat cured in a water bath at 50°C, and then removed from the water bath and dry cured at 200°C for two days prior to strength testing. This paper presents a combination of early age and longer term shrinkage measurements of UHSC that were used to characterize the total shrinkage that occurred during the curing process. Total shrinkage of fiber reinforced UHSC specimens that occurred during 30 days was 3,006 µ, with early age shrinkage (first 24 hours) contributing 58.5% of the total shrinkage.