Journal of Materials in Civil Engineering

The importance of sufficient masonry mortar joint-bond strength when a structure is subjected to in-plane and out-of-plane loads has been emphasized by several researchers. However, masonry unit/mortar bond strength is difficult to predict, and performing mechanical tests on existing masonry buildings to determine masonry flexural bond and shear bond strengths is generally not practical, such that predictive expressions relating the masonry flexural bond and shear bond strengths to other masonry properties are desirable. Although relationships between brick/mortar bond and compressive strength have been investigated previously by researchers located in many different parts of the world, most of these studies were laboratory-based and did not include testing of existing masonry buildings within their scope. The writers aimed to characterize the material properties of New Zealand unreinforced clay brick masonry (URM) buildings that were generally built between 1880 and 1930, with in situ testing and sample extraction performed on six heritage buildings. Masonry compression, bond wrench, and shear bond tests were undertaken. The experimental results indicate that the masonry flexural bond strength and bed-joint cohesion can be satisfactorily related to the mortar compressive strength.

Masonry material characteristics such as compression stress-strain behavior and the relationships between brick, mortar, and masonry compressive strengths are required for the detailed analysis and assessment of masonry structures. These properties have been investigated previously, but most past studies were laboratory based and did not include within their scope the testing of existing masonry buildings. This study aimed to characterize the compressive strength and the compression stress-strain relationship of vintage clay brick masonry used in New Zealand unreinforced masonry (URM)-bearing wall buildings that were generally constructed between 1880 and 1940. Testing was performed on 45 masonry prisms that were extracted from eight New Zealand historic URM buildings and on 75 masonry prisms that were constructed in the laboratory using 14 different brick/mortar combinations. It was found that the laboratory-constructed sample test results adequately replicated those from the field-extracted samples, and predictive equations and a numerical compression stress-strain model for use in the detailed seismic assessment of URM buildings were developed based on the experimental results.

To investigate the effect of reinforcement corrosion on the bond properties between concrete and reinforcing steel bar, pullout tests were conducted on a total of 20 specimens using corroded reinforcement bars embedded in concrete specimens. No. 3 (9.5-mm diameter) and No. 6 (19-mm diameter) bars corroded by an accelerated corrosion method were selected for testing. Two groups of corrosion specimens were prepared: one was whole-surface corroded (100%), and the other was partial-surface corroded with 40, 60, and 100% corrosion. Each group of specimens included four levels of corrosion: 3, 5, 10, and 15%. Results indicate that the tensile strength of steel bar decreases with the increase of corrosion level. Corrosion levels less than 3% present a minor tensile-strength reduction of approximately 3%, whereas the tensile strength may decrease to 75–90% when the corrosion level increases more than 10%. The critical bond strength and ultimate bond strength of corroded bars may increase slightly with corrosion level less than 3%, but tend to decrease as the corrosion level exceeds 3% and, likewise, to decrease with increasing corroded-surface percentage of steel bar. The range of partial-surface corrosion shows no significant effect on yield strength and ultimate strength of the steel bar. However, the critical bond strength and ultimate bond strength in a reinforcing steel bar decrease with the percentage of corroded surface for various corrosion levels when the corroded area increases from 40–100%.

In this study, a low-carbon rice husk ash (RHA) was used as a supplementary cementing material in cement mortars to evaluate its sulfate resistance in sodium and magnesium sulfate solutions. The sulfate resistance of these mixtures in terms of expansion and loss of compressive strength was determined using the standard test method.. The water to cementitious material ($\mathrm{w}/\mathrm{cm}$) ratio and RHA dosage in the mortars was varied from 0.40 to 0.57 and 0 to 15% (by mass), respectively. The results from this investigation suggest that all mortars with a w/cm ratio of 0.40 showed little deterioration, indicating their high sulfate resistance. For mortars with a $\mathrm{w}/\mathrm{cm}$ ratio of 0.48 and 0.57, the control mortars showed more deterioration than those with RHA. For mortars at any given $\mathrm{w}/\mathrm{cm}$ ratio, the sulfate resistance decreased with an increase in the RHA dosage. Though both sodium and magnesium sulfates caused significant deterioration in the specimens, the former caused increased expansions in the test specimens while the latter caused significant loss in compressive strength. The sulfate resistance of RHA mortars was comparable with that of silica fume mortars.

The aim of the work presented here was to quantify the mineralogical phases contained in a basic oxygen furnace slag (BOFS), and especially the hydraulic phases, so as to evaluate the reactivity of this material. The chemical and mineralogical characteristics of BOFS were analyzed. This slag was essentially composed of calcium, iron, silicon, and magnesium oxides contained in five main minerals: calcium silicate oxides ($\beta \text{-}{\mathrm{Ca}}_2{\mathrm{SiO}}_4$ and ${\mathrm{Ca}}_3{\mathrm{SiO}}_5$), a solid solution of calcium aluminum ferrite oxides (${\mathrm{Ca}}_2{\mathrm{Fe}}_{1.52}{\mathrm{Al}}_{0.48}{\mathrm{O}}_5$), a solid solution of magnesium iron oxides (MgO0.432FeO0.568), and free lime CaO. The Rietveld method was used to determine the amount of each mineral phase and led to the following mineralogical composition: $\beta \text{-}{\mathrm{Ca}}_2{\mathrm{SiO}}_4=32\%$, ${\mathrm{Ca}}_3{\mathrm{SiO}}_5=2\%$, ${\mathrm{Ca}}_2{\mathrm{Fe}}_{1.52}{\mathrm{Al}}_{0.48}{\mathrm{O}}_5=26\%$, ${\mathrm{MgO}}_{0.432}{\mathrm{FeO}}_{0.568}=22\%$, and $\mathrm{CaO}=18\%$. BOFS thus contained a significant amount of hydraulic phase (dicalcium silicate and free lime), which was confirmed by the study of its reactivity using a hydrated paste.

Permeability of open-graded asphalt mixes is defined as the ability to transmit fluids through the voids. The infiltration of water affects the durability and safety of pavement systems. Traditionally, an empirical approach, based on laboratory tests or on field measurements, is used to evaluate hydraulic permeability. In general, such an approach allows the ex post calculation of the drainage capability of the open-graded pavement. In order to evaluate the hydraulic permeability during the phase of mix design, in this paper a novel method is proposed, based on simulation of unsteady flow of water through open-graded mixture. In particular, a real sample of asphalt mix is simulated in the shape of a Marshall test sample. It is composed of a set of particles, selected according to the real grading, positioned in the space domain following the random sequence adsorption approach (RSA) and covered by a film of bitumen. The flow of water through the synthetical sample is simulated through the lattice Boltzmann method. In this method, the particles of water propagate and collide while moving on a lattice, obtained by discretizing the physical space. This lattice is formed by equidistant nodes, where each node corresponds to a void or to a solid. The velocity of the particles depends on a set of microscopic velocity vectors. Simulation results allow prediction of the permeability of open-graded pavement through a theoretical calculation based on the Kozeny-Carman equation. The model is validated using experimental tests.

This paper presents a three-dimensional (3D) image-based microstructural computational modeling framework to predict the thermoviscoelastic, thermoviscoplastic, and thermoviscodamage response of asphalt concrete. X-ray computed tomography is used to scan dense-graded asphalt concrete (DGA) to obtain slices and planar images, from which the 3D microstructure is reconstructed. Image processing techniques are used to enhance the quality of images in terms of phase identification and separation of particles. This microstructure is divided into two phases: aggregate and matrix. The aggregate phase is modeled as an elastic material and the matrix phase is modeled as a thermoviscoelastic, thermoviscoplastic, and thermodamage material. Stress-strain response, damage propagation, and the distributions of the viscoelastic and viscoplastic strains are predicted by performing virtual uniaxial and repeated creep-recovery tests of the developed 3D model of asphalt concrete. The effects of loading rate, temperature, and loading type on the thermomechanical response of asphalt concrete are investigated. In addition, the microscopic and macroscopic responses of DGA are compared with those of stone matrix asphalt (SMA). The results demonstrate that SMA can sustain higher strain levels at the microscopic level and higher macroscopic ultimate strength. The damage in SMA is more localized than in DGA. The microstructure-based framework presented in this paper can be used to offer insight on the influence of the distribution and properties of microscopic constituents on the macroscopic behavior of asphalt concrete.

To address the problem of steel corrosion, fiber-reinforced polymer (FRP) bars are often used as reinforcement in concrete structures. However, conventional FRP bars are characterized by linear elastic behavior that limits their efficacy in seismic structural applications. This paper investigates the fabrication and cyclic behavior of a relatively new class of composite material known as SMA-FRP that could be used as seismic reinforcement for concrete structures. The new composite comprises a high elongation resin matrix, embedded with superelastic NiTi shape memory alloy (SMA) wires as primary reinforcement. The SMA wires are used either with or without the addition of conventional fibers. The hysteretic nonlinear pseudoelastic behavior of SMA provides the new composite with features that conventional FRP lacks, such as ductility and energy dissipation capability. The experimental program carried out in this study starts with the training of SMA wires, and the investigation of the hysteretic behavior of several types of resin. Two types of SMA-FRP composite material are then fabricated and tested under uniaxial tensile cyclic loading. The first type of composite is reinforced with 100% SMA wires, while the second type is reinforced with hybrid fibers made of SMA and glass-FRP. Test results show ductile behavior of the SMA-FRP composite with no signs of fiber debonding. Fiber-based numerical models are then developed to capture the SMA-FRP composite cyclic response.

This article studies the durability of the calcium carbide residue (CCR) and fly ash (FA) stabilized silty clay against wetting and drying cycles to ascertain its performance in pavement applications. The durability test on the CCR-FA stabilized clay samples compacted on dry and wet sides of optimum was performed according to the ASTM. The mixture of CCR and FA can be used for soil stabilization instead of ordinary portland cement. The suitable ingredient of CCR, FA, and clay results in a moderately high strength and durability geomaterial. The durability against wetting and drying (w-d) cycles of the CCR stabilized clay is considered low according to the recommendations of the American Concrete Institute and the U.S. Army Corps of Engineers and is not accepted as a pavement material. The input FA at optimal content reacts with the excess $\mathrm{Ca}{(\mathrm{OH})}_2$ from the CCR, and hence a significant improvement of the strength and durability. The optimal FA content is found at about 20%. The strength analysis shows that the durability is directly related to the unsoaked strength (prior to the w-d cycles). Consequently, a relationship between the w-d cycle strength and unsoaked strength is proposed. It is useful for quick determination of unsoaked strength during mix design to attain the target strength at the design service life.

Experimental small-scale modeling of clay brick masonry for behavior up to failure under earthquake-type loads poses many challenges, such as manufacturing of small-scale bricks and creating masonry that not only meets necessary similitude laws but also accommodates the requirement of artificial mass for shake-table tests. In addition, the stress and modulus ratios should be unity for model and prototype masonry in all loading conditions. The suitability of the half-scale bricks, produced in the same manner as the prototype, was studied through several material tests on brick units and masonry assemblages. Tests for compressive strength, water absorption, and initial rate of absorption were conducted on brick units. Axial compression, shear, tension bond, flexure, and diagonal compression tests were performed on brick masonry assemblages. A reasonable agreement in strength and stiffness properties of model and prototype masonry was observed, despite the difference in compressive strengths of model and prototype brick units. These results validate the suitability of half-scale bricks to predict the behavior of prototype masonry assemblages up to failure under various loading conditions.

A multiphysics formulation for chloride diffusion in an RC beam with stress-induced damage quantifying the enhancement in chloride diffusivity due to damage is presented. An experimental investigation involving measurement of chloride profile was conducted on RC beams damaged under applied flexural stress. Numerical simulation of the RC beam is carried out using a two-dimensional finite-element approach incorporating the damage due to the applied stress, chloride binding, and the chloride diffusion in the model. Concrete is assumed to be a perfectly elastoplastic (Drucker-Prager) material and the steel as an elastoplastic (von Mises) material with hardening. Drucker-Prager parameters, cohesion $c$, and friction angle $\phi$ are obtained by calibrating numerical load-deflection ($P\text{-}\mathrm{\Delta }$) curve to an experimentally determined ($P\text{-}\mathrm{\Delta }$) plot for beams loaded in flexure. Defining a scalar damage index as the degradation in elastic modulus expressed in terms of total strains, the chloride transport problem is addressed, using an effective diffusion coefficient, $D_{\mathrm{eff}d}$, expressed as a function of the damage index and chloride binding and obtained by calibrating to data for chloride profiles as determined in flexurally damaged beams. Using the expressions for the effective diffusion coefficient, $D_{\mathrm{eff}d}$, the chloride profiles are shown to match the experimentally determined chloride profiles in beams damaged at various stress levels.

This paper investigates the fresh, mechanical, and durability characteristics of self-consolidating concrete incorporating recycled asphalt pavements (SCCRAP). A total of 12 concrete mixtures were prepared and tested. Mixtures were divided into three different groups, with constant water to cementitious materials ratio of 0.37, based on the recycled asphalt pavement (RAP) content: 0, 25, and 50% coarse aggregate replaced by RAP. All mixtures were prepared to achieve a target slump flow equal to or higher than 500 mm (24 in.). The control mixture for each group was prepared with 100 percent portland cement, whereas all other mixtures were designed to have up to 70 percent of the portland cement replaced by a combination of supplementary cementitious materials (SCMs), such as class C fly ash and granulated blast furnace slag. The properties of fresh concrete investigated in this study included flowability, deformability, filling capacity, and resistance to segregation. In addition, the compressive strength at 3, 14, and 28 days; the tensile strength; and the unrestrained shrinkage up to 80 days were investigated. Using up to 70 percent slag as partial replacement of cement in concrete mixtures developed a 28-day compressive strength less than that of the control mixture by 26 and 49% for RAP content of 25 and 50%, respectively. Increasing the RAP content from 0 to 25 and 50% caused the split tensile strength of all mixtures to decrease significantly. Based on the results obtained in this study, it is not recommended to replace the coarse aggregate in self-consolidating concrete with more than 25 percent RAP.

Polyethylene pipes are commonly used for new and existing pipeline systems. The stresses developed in the polyethylene pipes affect the behavior of other pipe materials in the system to which they are connected. The overall behavior of the pipeline depends on the soil-pipe interaction characteristics; however, understanding and modeling the polyethylene pipe stresses as a first step without the influence of other factors is necessary. Laboratory tests were performed to investigate the time-dependent stress relaxation behavior of polyethylene pipe under mechanical and thermal loading conditions. Analytical methods using convolution integrals and numerical modeling using finite elements were used to model stress relaxation behavior monitored during the tests performed. The results show that the pipe thermal stresses are significantly less than the design stresses typically used by utility companies. In addition, linearly viscoelastic material characterization can be used to predict polyethylene pipe behavior for the range of stresses expected to occur in buried polyethylene pipes exposed to thermal loading. This article presents the test results as well as analytical and numerical results for modeling and predicting stresses in polyethylene pipes.

Cracking failure in asphalt binder in winter has always been one of the most serious problems in pavement structures. Classical fracture mechanics is the most widely used method to analyze the initiation and propagation of cracks. In this paper, a new modeling and computational tool—namely, the phase-field method—is proposed for modeling the Mode I cracking failure in asphalt binder. This method describes the microstructure using a phase-field variable that assumes 1 in the intact solid and $-1$ in the crack region. The fracture toughness is modeled as the surface energy stored in the diffuse interface between the intact solid and crack void. To account for the growth of cracks, a nonconserved Allen-Cahn equation is adopted to evolve the phase-field variable. The energy-based formulation of the phase-field method handles the competition between the growth of surface energy and release of elastic energy in a natural way: the crack propagation is a result of the energy minimization in the direction of the steepest descent. Both the linear elasticity and phase-field equation are solved in a unified finite-element framework, which is implemented in commercial software. The Mode I crack simulation is performed for validation. It was discovered that the onset of crack propagation agrees very well with the Griffith criterion and experimental results.

Alkali-activated binders (AAB) or geopolymers are new ceramic materials with the potential to replace portland cement in a wide range of applications, from immobilization of heavy metals to concretes for civil engineering. They rely on the alkaline activation of aluminosilicates, such as blast furnace slag (BFS), pulverized fly ash (PFA), and metakaolin (MK). Despite their high mechanical strength and chemical durability, geopolymer concretes are in many cases marked with high porosity and permeability, which could negatively affect the performance or long-term durability of concretes. This paper employs the Andreasen particle packing method, commonly used for ceramic materials, to improve the geopolymer formulations studied on the development of micro-concretes. Three parameters were investigated: (1) the Andreasen packing factor q, 0.21, 0.235, and 0.26, which alter particle size distribution of aggregates; (2) the solution to solids rate, 1.3, 1.4, and 1.5; and (3) the type of aggregates, either glass or quartz. The influence of these parameters on mechanical strength, in addition to porosity and apparent density, were determined. Results have shown that the Andreasen method may be used to change the rheology and, therefore, develop different geopolymer mixes. In the particular case of the development of geopolymer floor tiles, the best formulation is the one with a solution to solid rate of 1.4, Andreasen packing factor of 0.235, and quartz aggregate.

The industry standard currently accepted method for assessing the resistance of concrete to penetration of chloride ions is commonly known as the rapid chloride permeability (RCP) test. The test is time-consuming and laborious and the user must be extremely careful to ensure accuracy, making it problematic for inclusion as a performance variable in a concrete specification. A potential alternative to the RCP test is the surface resistivity (SR) test, a method that is dramatically easier, faster, and requires far less special care than the RCP test. The research reported herein was directed toward determining a correlation between RCP and SR test measurements for Tennessee bridge deck concrete (based on cylinders collected from concrete bridge decks being constructed across the state) and evaluating the appropriateness of the SR test as an alternative to the RCP test for inclusion in a specification for bridge deck concrete. Results of the testing showed a clear correlation between the two methods and identified potential limits for possible inclusion as a performance requirement in a specification.

An experimental study was undertaken to develop an extension of Mohr-Coulomb and Newman models to predict the failure of concrete subjected to elevated temperatures. Concrete specimens of $83\times 166\text{-mm}$ dimensions were prepared and subjected to various temperature levels of 300, 500, and 700°C. The tests were carried out in triaxial cell using various confining stress levels. The applied confining pressures varied between 1.4 and 24 MPa, corresponding to 3 and 54% of the uniaxial compressive strength. Test results indicated that the increase in temperature and/or confining pressure lead to a significant change in the mechanical properties of concrete. Furthermore, the Mohr-Coloumb and Newman models did not provide good fitting of the experimental data obtained on concrete subjected to high temperature of up to 700°C. A dehydrate index is introduced and used to define new variables in the existing models. The modified models are shown to adequately predict the residual strength of concrete that has been subjected to high temperatures.

An experimental investigation was conducted to study the shear strength of full-scale beams constructed with both chemically based self-consolidating concrete (SCC) and conventional concrete (CC). This experimental program consisted of 12 beams without stirrups with three different longitudinal reinforcement ratios. The beams were tested under a simply supported four-point loading condition. The experimental shear strengths of the beams were compared with the shear provisions of both U.S. and international design codes. Furthermore, the shear strengths of the beams were evaluated based on fracture mechanics approaches, modified compression field theory (MCFT), and a shear database of CC specimens. Results of this study show that the SCC possesses comparable shear strength to the CC.

One approach to produce environmentally friendly and cost effective asphalt mixtures is to use more readily available recycled materials like reclaimed asphalt pavement (RAP) and rubber. In this study, ground tire rubber (GTR) and treated ground tire rubber (TGTR) were added to an asphalt binder and to high RAP content mixtures. Rutting and fatigue characteristics of the modified binder were evaluated.GTR and TGTR improved the rutting and fatigue performance of the asphalt binders. A suspension agent helped reduce the degree of separation. GTR was introduced into the binder and the resulting rubberized binder was used to prepare the mixtures. The TGTR was directly added to the mixture. TGTR mixtures were mixed and compacted at lower temperatures compared with GTR mixtures. The dynamic modulus, reflective cracking performance, low temperature cracking, and rutting and moisture susceptibility were evaluated for the mixtures. GTR and TGTR made improved resistance to rutting, moisture susceptibility, and low temperature cracking. According to the Texas overlay test, the GTR and TGTR might not improve the mixture’s resistance to reflective cracking.

Beaver Slide is on the Dalton Highway near 177.8 km (110.5 mi), and it is downhill when heading north. The road gradient is approximately 11% and the road prism is on a side hill. Each year, there are soft spots that usually appear in late April and remain all summer, which are also called “frost boils” by engineers at the Alaska Department of Transportation and Public Facilities (AKDOT&PF). The frost boils have resulted in extremely unsafe driving conditions and frequent accidents. Past repair efforts indicate conventional road construction methods do not work. A new type of geosynthetic wicking fabric has been recently developed that has a high specific surface area (consequently high wettability and high capillary action) and high directional permittivity. Preliminary laboratory tests indicate it has great promise as a cost-effective means to solve the frost heave-related problems on northern road systems. This study verifies the effectiveness of the wicking fabric to mitigate frost boils in Alaskan pavements. A test section was built at the Beaver Slide area of the Dalton Highway with installation of two layers of wicking fabric. The test section was instrumented with moisture and temperature sensors to measure the temperature and moisture variations for two years. Results were analyzed to evaluate the effectiveness of the wicking fabric to mitigate the frost boils in Alaskan pavements.

Laminated bamboo lumber (LBL) is regarded as an alternative framing material for the construction industry. However, there is limited knowledge of its behavior in connection with commonly used sheathing material, such as oriented strand board (OSB). This study characterized the lateral load carrying capacity of LBL-OSB connections and studied the applicability of the yield models presented in the national design specifications to LBL connections. Two different connection geometries, edge and plate, which were representative of those present in a wall, were analyzed. The strength of the connections was characterized using monotonic testing. After the destructive testing, portions of the framing and sheathing materials from the samples were further evaluated for dowel bearing strength. Experimental results indicate that the LBL-OSB connections have similar lateral load carrying capacity as conventional Douglas fir-OSB connections. No statistical significance was observed in the strength differences of edge and plate connection geometries. The results further indicated that existing yield models used for design of nailed connections can predict the capacity and the mode of yielding for edge connection geometry between OSB sheathing and LBL framing members of grade and dimensions considered in this study, provided that the dowel bearing capacity of the materials is known.

While the recycling of asphalt shingles is beneficial in reducing the consumption of virgin materials, pavement performance should not be compromised. One major concern with recycled asphalt shingles (RAS) relates to the variability in the properties of the recycled materials originating from different sources. In addition, the rheological properties of RAS have not been evaluated as well as its influence on the virgin binder when used in asphalt mixtures. Therefore, the objectives of this study were to characterize the rheological properties and molecular fractions of RAS materials sampled from different sources around the country. In addition, the influence of RAS on the Superpave Performance Grade (PG) of the binder was investigated. Results of the experimental program indicated that the asphalt cement (AC) content in tear-off shingles was consistent among different RAS sources across the country. However, AC content in manufacturer waste shingles was noticeably lower than in tear-off shingles. In addition, all extracted RAS binders were graded as PG 118 or higher using the Superpave binder specification system but the low temperature grade was not measurable due to the high stiffness of the binder. This stiff behavior is due to the binder used in shingle manufacturing, which is an air-blown asphalt binder with stiff characteristics and low elongation properties. Results showed that at a RAS content of up to 5%, the high temperature grade of the blends was increased by one to seven grades and the low temperature grade was increased by one grade. The use of binder blending charts is recommended to account for the influence of RAS in the mix design. At a RAS content of 10%, the binder blends did not pass the Superpave criterion at low temperature.

The amount of solar energy emitted back from conventional asphalt pavement contributes to the phenomenon of urban heat island (UHI), and the current work was focused on studying the thermal behavior of asphalt pavement developed as a coating material from wasted tile. The surface temperature of asphalt surface with and without coating material for ambient temperature and underground soil temperature was studied. Results showed that the application of developed coating materials could reduce the surface temperature of asphalt pavement up to 4.4°C. Rainfall also played a significant role as a natural coolant during the experimental run by maintaining the surface temperature continuously for 2 days after the rainfall event, with an average surface temperature of 41.9°C. The underground soil temperature of the coated surface showed reduction in the range of 0.8–1.2°C throughout the day. The coating materials achieved their efficiency in reducing the emitted radiation only during noontime and the results show that the developed coating materials have true potential to serve as cool pavement to combat UHI effects.

The bond behavior of deformed reinforcing bars, which is important to the assessment and design of reinforced concrete structures, is greatly influenced by the stress state in concrete. Because the effect of biaxial lateral tensile-compressive stresses on the bond behavior of deformed bars is seldom studied, an experimental investigation is presented in this paper. A total of 252 pull-out specimens with different strengths of concrete, bar diameters, and combinations of lateral tensile-compressive stresses were included in the test. The results show that the failure mode of specimens with deformed bars is influenced by the strength of concrete, ratio of the cover depth to bar diameter $c/D$, and the coupling effect of lateral stresses $\zeta (=p_t/f_t+p_c/f_{cu})$. The bond strength and the slip at the peak bond stress decrease by increasing $\zeta$, whereas the deteriorating ratio depends on the strength of concrete and $c/D$ for specimens failed by pull-out and splitting, respectively. Regardless of $\zeta$, the ratio of the residual and ultimate bond strength for the specimens in pullout failure basically keeps constant. An empirical bond stress-slip relationship is proposed. For different strengths of concrete, bar diameters, and combinations of lateral stresses, the proposed bond stress-slip relationship is in good agreement with experimental results.

Laboratory tests have been carried out in order to evaluate the improvement in engineering properties relevant to highway design and construction obtained when clayey subgrade soils are stabilized with lime or fly ash. The experimental program included California bearing ratio (CBR) tests to evaluate the bearing strength of stabilized soils used as working platforms during highway construction. The admixture of lime or fly ash caused an increase in the plasticity limit, while both the liquid limit and the plasticity index of the soils have been reduced. Substantial increases in the California bearing ratio value, higher than those of the soil–fly ash mixtures, have been obtained when the soil samples were mixed with lime. The swelling after a 4-day soaking period has been reduced with the addition of both additive materials. The increase in optimum moisture content acts subsidiarily to the increased CBR value, particularly at high lime or fly ash percentages. An analogous effect has been found for the maximum dry density reduction.

A fluid-pressured test has been developed as an alternative to measure tensile strength of concrete. This test method covers the determination of the tensile strength of cylindrical concrete specimens with a centered internal hole where a radial internal fluid pressure is applied until failure occurs. This loading condition induces tangential stresses on the specimen; the maximum fluid pressure sustained by the specimen is affected by appropriate geometric factors to obtain a measurement of the tensile strength. Preliminary experimental data suggests that the tensile strength measured with the proposed method is about 17% greater than the tensile strength obtained from splitting tensile tests. Additionally, results of the tensile pressure strength were on average 11% of the compressive strength.

The main objective of this study was to investigate the impact of longer creep-recovery times on the percent recovery ($R$) and the nonrecoverable compliance ($J_{nr}$) of three asphalt cements (AC), or binders, modified with (1) styrene-butadiene-styrene (SBS) copolymer, (2) polyphosphoric acid (PPA), and (3) SBS+PPA. The base material is a $50/70$ pen-grade (PG 64-xx) asphalt binder and the modified asphalt binders have the same high-temperature performance grade (PG 76-xx). The impact of longer creep-recovery times was addressed by calculating the percent recovery and the nonrecoverable compliance ratios at the test temperatures of 70°C and 76°C. The multiple stress creep and recovery (MSCR) test was used to determine the $R$ and $J_{nr}$ values at the stress levels of 0.1 and 3.2 kPa. Two creep-recovery times were used, namely, $1/9$ and $2/18\mathrm{s}$. The highest $R$ values and the lowest $J_{nr}$ values can be found in the AC+PPA formulation. The increase in both creep-recovery times caused less impact on the rutting susceptibility of the AC+SBS+PPA than the AC+SBS and the AC+PPA under the same MSCR test conditions.

Concrete is a composite material consisting of mortar and coarse aggregates. The use of recycled aggregates in concrete is increasing gradually. Recycled coarse aggregates are highly porous and often contain microcracks and weak interfacial transition zone (ITZ). Therefore, the recycled aggregates are weaker than natural coarse aggregate and their modulus of elasticity (E) is expected to be lower than that of natural coarse aggregate. This paper examines and presents the existence of dividing strength in concrete containing recycled coarse aggregate. In this study 192 concrete cylinders ($100\mathrm{\varphi }\times 200\mathrm{mm}$) and 192 mortar cubes ($50\times 50\times 50\mathrm{mm}$) were cast and tested at 28 days for compressive strengths of natural aggregate concretes (NAC) and recycled aggregate concretes (RAC). In the case of NAC, the linear relationship between the compressive strength of concrete and that of mortar is observed. However, in the case of RAC, a distinct two-stage relationship between concrete strength and mortar strength is observed indicating the existence of the dividing strength of recycled aggregate concrete. This paper emphasizes that more research needs to be conducted in the existence of dividing strength as the properties of recycled coarse aggregates very quite substantially depending on the contents.

Supplementary cementitious materials (SCMs) have been used in portland cement concrete pavements (PCCP) to increase their resistance to deterioration mechanisms, such as alkali-silica reaction (ASR), freeze and thaw, and permeability. In addition, SCMs are mostly by-products that can effectively reduce material cost and improve concrete sustainability. This paper presents the results of an experimental investigation carried out to evaluate the effect of Class C fly ash, Class F fly ash, and ground granulated blast furnace slag (GGBFS) on the performance of PCCP. Laboratory testing of multiple mixes with different combinations and percentages of SCMs is presented. This testing includes slump, unit weight, air content, time of setting, compressive strength, flexural strength, alkali-silica reactivity, freeze/thaw, length change, chloride ion penetration, and wet/dry test specified by Nebraska Department of Roads (NDOR). Field applications of four candidate mixes at two separate locations are also presented. Test results from laboratory and field investigations indicated that using a combination of Class C fly ash (15–20%) and Class F fly ash (20–25%), or all three SCMs in the range of 15–20% each, improves concrete durability and overall performance.