Journal of Materials in Civil Engineering

The paper is devoted to the cracking and deformability analysis of steel reinforced concrete beams strengthened with externally bonded carbon fiber reinforced polymer (CFRP) sheets. A theoretical nonlinear model, derived from a cracking analysis founded on slip and bond stresses, is adopted. The model takes into account both the tension stiffening effects of the concrete and the force transfer between the concrete and the CFRP sheet at the interface. A local bond-slip law—defined by experimental tests, carried out on concrete specimens strengthened with CFRP sheets—is adopted in the model. The slip between the concrete and the traditional steel bars is also considered. Theoretical predictions, in terms of crack width, curvature, and deflections, are compared with available experimental results and predictions of traditional models, usually adopted for design purposes. Obtained results are presented and discussed.

A procedure for assessing stiffness variations due to damaging and retrofitting of reinforced concrete beams is presented in this paper. This procedure is based on modal analysis and testing. Two beams were subjected to cyclic loading at increasing load levels, in order to induce in them increasing cracking patterns. The beams were then retrofitted by externally bonded carbon fiber reinforced polymer sheets. Modal tests were carried out after each loading–unloading cycle. A theoretical model was developed, in order to simulate the behavior of the beams in each situation. This model is based on the concepts of fracture mechanics to evaluate the stiffness of cracked beam elements, with and without external strengthening. The theoretical results are in good agreement with the experimental ones. The research suggests that dynamic testing can be used to obtain useful information about the effectiveness of the strengthening system.

The oldest cast iron arch bridge built in 1852 in Venice exhibits serious deterioration due to corrosion and cracking of its members. The Municipality accepted a proposal to strengthen it with Aramid fiber reinforced polymers (AFRP) materials. The AFRP materials application aims to arrest cracks and reduce the structure’s vulnerability to impact by boats. Tests have already been performed on structural cast iron beams taken from similar cast iron bridges dismantled. Results from four point bending tests showed an increase in strength and a different fracture mode depending on FRP application. Charpy tests showed an increased fracture energy in specimens strengthened with FRP and primer. Utilization of bidirectional and triaxial fabrics was discussed. However this paper is particularly focused on nondestructive testing following the FRP application. Nondestructive testing has been planned both for laboratory test specimens and for a long term monitoring program. Artificial defects, embedded during manufacturing in some test specimens, have been analyzed using the pulsed echo ultrasonic technique, in order to compare the resolving power of different ultrasonic frequencies and probe arrangements. Furthermore, a long term monitoring program has been planned in order to assess bonding performance using ultrasonic and pulloff tests on the overall strengthening and on some test specimens placed in the same environment.

Glass fiber reinforced plastics (GFRP) frequently are used for reinforcement of engineered concrete structures. However, the effectiveness of GFRP as reinforcement is reduced because of their susceptibility to stress corrosion. To estimate damage evolution of composite reinforcement as a result of stress corrosion, an acoustic emission (AE) technique was used. It has been stated that stress corrosion takes place both in acid and alkaline environments; however, the damages are different. The waveform of acoustic emission signals can be used to indicate different failure mechanisms. There is a relationship between the number of AE events and compliance changes as a result of stress corrosion cracking. The number of AE events may be used to predict the service time of composite reinforced of concrete structures.

The first decay shown by masonry subjected to an aggressive environment is the loss of surface material. The great randomness of this kind of decay phenomenon suggests studying it from a probabilistic point of view. Here, the evolution of decay in stone masonry has been investigated by applying two different approaches on experimental data collected on on-site models. Since the results are very similar, the choice of approach depends only on the available data and the monitoring time.

Removing heat from mass concrete at initial construction is important for assuring the quality of the concrete after curing. It serves two main purposes, preventing the excessive stress development within the concrete when the difference between the surface and interior temperature becomes high and keeping the temperature within the concrete below a certain critical temperature or as low as possible. The control of the temperature within a mass concrete structure can be attained by various means depending on the situation. In this paper, cooling in mass concrete using a lattice of water pipes is analyzed based on the Fourier–Biot heat conduction equation. Exact solution of the temperature field within the concrete is found by integrating concrete material properties, heat generation rate due to hydration, and characteristics of the cooling process. The analytic result is applied to understand reported thermocouple readings in a large concrete footing cooled in a pipe lattice. The model is applicable for establishing technical guideline on heat removal from mass concrete. Possible ways on keeping the temperature low within the concrete are suggested for future practices.

The flexural fatigue characteristics of two different shotcreted engineered cementitious composites (ECCs) containing polyvinyl alcohol (PVA) and polyethylene (PE) fibers respectively were tested under four-point bending. The failure mechanisms and characteristics were investigated in comparison with a shotcreted steel fiber reinforced cement. The results showed that both ECCs exhibited a unique fatigue stress–life relationship that is represented by a bilinear function on a semilogarithmic scale. The failure mechanism of ECCs involved the development of multiple cracks, and the number of cracks was higher when the fatigue stress level was higher. The difference in crack opening displacement results from their different fiber bridging characteristics. PVA fibers tended to break under fatigue, while PE fibers tended to pullout. Although PE-ECC provided more cracks at the same fatigue stress, level, PVA-ECC showed larger deformation than PE-ECC because each crack width of PE-ECC was smaller than that of PVA-ECC. The deformation is shown to be governed by the number of cracks as well as the crack width, where the fiber bridging characteristics are related to either fiber rupture or fiber pullout.

The superior performing asphalt pavement (Superpave) hot mix asphalt (HMA) mix design system was a principal development of the Strategic Highway Research Program (SHRP). In the Superpave mix design system, the Superpave gyratory compactor (SGC) was developed as a laboratory HMA compactor, targeted at better simulating the field compaction of HMA mixes. All $\mathrm{SGCs}$ are required to meet the American Association of State Highway and Transportation Officials (AASHTO) T312 specification parameter requirement of external gyration angle $(1.25\pm 0.02°)$. Numerous agencies have reported significant differences in the HMA bulk specific gravity $\left(G_{\mathrm{mb}}\right)$ of the same HMA mix compacted in different $\mathrm{SGCs}$. These differences are hypothesized to be, in part, due to different internal gyration angles between $\mathrm{SGCs}$. In response, a dynamic angle verification (DAV) procedure has been used to measure and verify the internal gyration angle during compaction. $\mathrm{SGCs}$ located in the central and district Mississippi Department of Transportation laboratories were evaluated with the DAV procedure to determine the internal gyration angle and the resulting $G_{\mathrm{mb}}$ values. Substantial differences in the internal and external gyration angles, as well as the top and bottom DAV determined internal angles, were found for many of the $\mathrm{SGCs}$ evaluated.

Monotonic load tests have been conducted on plain and fiber-reinforced concrete slabs on ground to monitor the effect of fiber type and dosage on the strength properties of concrete slabs. The results revealed that simple material tests do not always successfully predict the contribution of fibers in cases where structural geometry and boundary considerations control redistribution of load. The tensile cracking loads of plain and fibrous slabs were found to be similar, which had previously been reported for small- scale fiber specimens, but, there was a significant increase in the flexural strength of fiber-reinforced concrete slabs, relative to plain concrete slabs. Companion beam flexural strength tests also significantly underestimated the concrete slab flexural strength for both the plain and fibrous concrete slabs. The addition of fibers increased the collapse load of slabs, with the key factors affecting the magnitude of the collapse load being fiber type and quantity. Strain and deflection profile measurements showed that fibers assisted in crack propagation resistance, crack bridging, and load redistribution. The shape of the load deflection curves indicated that the synthetic and the steel-fiber-reinforced concrete slabs behaved similarly at different stages of cracking.

The emergence of polymeric mortars as a class of materials with applications in civil engineering requires a systematic study of their properties, including mechanical strength and durability under severe environmental conditions. This study reports results based on tests of polymeric mortars, both with epoxy and polyester resins, after exposure to (1) immersion both in distilled and in salt water, (2) salt fog spray cycles ($8h$ of salt fog, followed by $16h$ drying, at $35°C$), and (3) temperature cycles [$12h$ at 20 and $50°C$, respectively, with relative humidity (RH) kept at 80%]. Additional tests for humidity cycles at fixed temperature and ultraviolet rays are reported elsewhere. Moisture absorption is analyzed based on mass changes for submerged specimens and Fickian type behavior evaluated. Compressive and bending strength degradation, as well as increase of brittleness, are examined for these accelerated actions and preliminary interpretation advanced. The relative severity of the effects is graphically displayed, tabulated, and analyzed. Brittleness increases more rapidly, under salt fog, for epoxy mortar and bending strength reduction at $10\text{,}000h$ is also higher (50%) for epoxy mortar than for polyester mortar (32%). Thermal cycles also provoked greater deterioration of bending strength on epoxy mortars. Compressive tests led to results of similar tendency, but with smaller differences.

This paper addresses issues of machine compliance and instrumentation that affect the measurement of asphalt concrete material properties in the laboratory. Accurate determination of fundamental material properties is becoming increasingly important as the asphalt industry moves toward more mechanistic design procedures. This issue is particularly timely for the simple performance test and American Association of State Highway and Transportation Officials 2002 design guide that require the measurement of dynamic modulus, phase angle, and creep. The primary objective of this paper is to increase the awareness of the possible existence of these issues in the laboratory and the importance of attending to them appropriately. Machine compliance was found to affect the strains actually occurring in the specimen under various loading conditions, resulting in differences of several magnitudes between dynamic modulus values measured by the actuator and by surface-mounted deformation transducers. Instrumentation issues resulted in errors greater than 10% in the measurement of dynamic modulus for the mixtures studied and caused irrational trends in phase angle values as a function of frequency. Creep compliance testing was also found to be affected by instrumentation issues.

Cementitious materials have traditionally not been economically viable for most landfill containment systems. Conventional liners have been made with clay and high-density polyethylene membranes, supporting packed aggregate layers. This paper describes an alternative technology in which low-cost concrete liners may be constructed, making use of materials, which are considered to be wastes by their primary producers. Many materials that have the potential for use either as binder or as aggregate materials for concrete currently form part of the United Kingdom landfill inventory. Although unattractive for use as structural concrete, they offer considerable utility for landfill liner applications. Recent increases in disposal costs including the introduction of the landfill tax have, however, made low cost low strength mixes a financially attractive option as a barrier for landfill leachate containment. In this paper the required properties of cementitious mixes for this purpose are discussed. The results of an extensive investigation into potential mixes using various mineral wastes are presented and the measured properties are compared with those, which are required. All of the mixes, which have been investigated, contain large amounts of secondary materials. If these materials were treated as wastes their disposal costs would be high, so the mixes may be designated “negative cost mixes.” The results indicate that some of these mixes are well suited to this application.

Permeability is an important property that influences the performance of hot-mix asphalt (HMA). It is a function of compaction effort, and several properties of HMA such as asphalt content, and the shape and size distribution of aggregates. Due to the different laboratory and field methods for measuring permeability, and the interaction among the factors that influence its value, it would be difficult to develop an analytical equation that accurately relates permeability to all factors contributing to HMA permeability. This paper presents a simple equation for approximating the permeability of asphalt mixes. It utilizes the percent air voids and surface area of aggregates. The equation is empirical but it is derived based on the well-known Kozeny–Carman equation for calculating the permeability of granular materials. The developed equation was used successfully to fit permeability data collected from several studies that carried field and laboratory measurements of HMA permeability. A finite element model was developed to investigate the influence of the gradient of percent air voids in HMA on water flow patterns. The x-ray computed tomography was used to measure the percent air void gradients among sublayers of the asphalt mix. The permeability of these sublayers was calculated using the developed equation, and used as an input to the finite element model. The simulation results show that air void gradients in HMA encourage lateral flow in the horizontal direction and reduce the flow in the vertical direction.

Initially, the paper describes methods currently used for strength and erosion resistance testing of earth blocks. Following this, an experimental study undertaken to assess the influence of test procedure and specimen geometry on strength and erosion characteristics is presented. Cement stabilized pressed earth blocks were fabricated using different blended soils and compacted using a constant volume manual press. The effects of specimen geometry on experimental compressive strength are described and aspect ratio correction factors for unconfined unit strength outlined. Proposals for a unified approach to compression strength testing are also suggested. Bending strength testing is commonly used as an indirect method of strength assessment, as it is more readily suited to in-situ quality control testing than compression testing. The experimental correlation between compressive and bending strengths is presented. Results of compression tests on masonry walls are also presented together recommendations for design. Finally, the influence of test method and specimen geometry on erosion resistance and the correlation with block strength is discussed.

The research has been undertaken to determine the strength and quality of concrete material used to build various types of structures in various localities in the city of Istanbul, located within the first-degree disastrous area for a potential earthquake risk. Concrete core samples collected from a total of 244 structures (buildings, industrial, and governmental structures), for which the construction details, such as the production type (cast in place and/or ready mixed) and class of concrete material are known, have been tested for their compressive strength. Statistical analyses of the collected data show that the tested core samples have equivalent specified strength of between 1.61 and $70.05N/{\mathrm{mm}}^2$. The mean value for a total of 1,892 characteristic strength values has been found to be $22.01N/{\mathrm{mm}}^2$ with a standard deviation value of $9.99N/{\mathrm{mm}}^2$. The statistical results obtained using the production type and class (C14, C16, C18, C20, C25, and C30) of concrete indicate that the strength quality of both cast-in-place and ready-mixed concrete is, in general, quite far away from meeting the required concrete strength. Although ready-mixed concrete gives better values, the results show that approximately 42% of all the analyzed structures are below the quality required to build the structures safely.