Showing papers in "Journal of Materials in Civil Engineering in 2014"

Factors Affecting Improvement of Engineering Properties of MICP-Treated Soil Catalyzed by Bacteria and Urease

Abstract: Microbial induced calcite precipitation (MICP) is one of the potential methods for improvement of engineering properties of soil. A laboratory study was conducted to investigate the influen...

Reclaimed Asphalt Pavement and Recycled Concrete Aggregate Blends in Pavement Subbases: Laboratory and Field Evaluation

Abstract: In recent years, efforts have been made to incorporate reclaimed asphalt pavement (RAP) into pavement base or subbase applications by means of cement binder stabilization. This approach, however, may not be an environmentally friendly solution due to the high carbon footprint involved in the production of Portland cement. Recycled concrete aggregate (RCA), on the other hand, has been widely accepted in pavement applications. The sustainable solution of blending RAP with RCA was investigated in this research in an attempt to facilitate the usage of this blend as an alternative pavement subbase material. An extensive suite of geotechnical laboratory tests was undertaken on RAP with contents of 100, 50, 30 and 15% in blends with RCA. Results of the research study indicated that RAP/RCA blends with a low 15% RAP content meet the repeated load triaxial requirements for use in pavement subbase layers. Results of field performance of a pavement subbase constructed with untreated 100% RAP, at a private haul road field-demonstration site, confirmed that it had insufficient strength requirements to meet local road-authority pavement-subbase requirements. RAP and RAP/RCA blends, although found in this study to be not fully compliant with the local road-authorities requirements, could be potentially considered for lower traffic usage, such as haul roads and footpaths.

Bond Performance between Ultrahigh-Performance Concrete and Normal-Strength Concrete

Abstract: Ultrahigh-performance concrete (UHPC) exhibits several properties that make it appropriate for the rehabilitation of concrete structures. In this investigation, the application is focused on bridge deck overlays, but the study is equally applicable to other rehabilitation applications. Its negligible permeability makes this material suitable as a protective barrier that prevents any water or chemical penetration into the substrate. In addition, its ultra-high compressive strength and post-cracking tensile capacity could provide an improvement to the bearing capacity. However, for extensive acceptance, it has to be demonstrated that the bond between UHPC and normal strength concrete (NSC) offers a good long-term performance under a variety of operating conditions. The UHPC-NSC interface can experience high tensile, shear, and compressive stresses at both early and later life stages and the environmental conditions inherent to the operating environment. The success of the rehabilitation will depend ...

Aging Influence on Rheology Properties of Petroleum-Based Asphalt Modified with Biobinder

Abstract: This paper aims to investigate the viability of using swine waste binder to improve the rheological properties of bituminous asphalt binder. Due to rising bituminous asphalt binder costs, diminishing reserves of crude oil from which asphalt binder is derived, and the gradual paradigm shift toward more environmentally friendly and energy efficient hot-mix asphalt (HMA) mixtures, the asphalt pavement industry is exploring different sustainable alternative binders. Biobinder has the potential to partially or fully replace typical crude-based asphalt. In this paper, biobinder from swine manure is produced by thermochemical liquefaction process at 380°C and 40 MPa (approximately 400 atm) pressure in the absence of oxygen. A Superpave PG 64-22 is then modified with 5% biobinder by total weight of asphalt binder to produce the biobinder. Samples of the base asphalt binder (nonmodified PG 64-22) and samples of asphalt modified with biobinder are characterized by running the Superpave rotational viscosity ...

Influence of Wet-Dry Cycles on Compressive Strength of Calcium Carbide Residue–Fly Ash Stabilized Clay

Abstract: 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 CaðOHÞ2 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 thew-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. DOI: 10.1061/(ASCE)MT.1943-5533.0000853. © 2014 American Society of Civil Engineers.

Properties of Two Model Soils Stabilized with Different Blends and Contents of GGBS, MgO, Lime, and PC

Abstract: This paper addresses the use of ground granulated blast furnace slag (GGBS) and reactive magnesia (MgO) blends for soil stabilization, comparing them with GGBS-lime blends and Portland cement (PC) for enhanced technical performance. A range of tests were conducted to investigate the properties of stabilized soils, including unconfined compressive strength (UCS), permeability, and microstructural analyses by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The influence of GGBS:MgO ratio, binder content, soil type, and curing period were addressed. The UCS results revealed that GGBS-MgO was more efficient than GGBS-lime as a binder for soil stabilization, with an optimum MgO content in the range of 5–20% of the blends content, varying with binder content and curing age. The 28-day UCS values of the optimum GGBS-MgO mixes were up to almost four times higher than that of corresponding PC mixes. The microstructural analyses showed the hydrotalcite was produced during the GGBS hydr...

Biochar Sequestration in Lime-Slag Treated Synthetic Soils: A Green Approach to Ground Improvement

Abstract: Unconfined compressive strength (UCS) of synthetic biochar mixed clays (BMC) treated with lime-GGBS has been investigated. Biochar utilized in this study was produced from the slow pyrolysis of green waste residue. Treated biochar mixed clays have also been tested for microstructural and mineralogical developments. Results of this study showed that a lime content of 2 wt%, which is much lower than the conventionally used 10 wt% lime for synthetic clay, can be effectively incorporated to improve BMCs. X-ray Diffraction analysis carried out on treated BMCs showed the development of cementitious minerals (C─S─H, ettringite). Scanning Electron Microscopy with Energy Dispersive Spectrum (EDS) enabled identification of three separate types of microstructural interactions between biochar and soil particles, namely interface cementation, surface deposition and pore space filling by cementitious minerals, all of which are responsible for the enhancement of UCS with curing.

Dicyclopentadiene and Sodium Silicate Microencapsulation for Self-Healing of Concrete

Abstract: Considerable interest has been directed in recent years toward the use of self-healing materials in concrete. The concept of microcapsule healing is based on a healing agent being encapsulated and embedded in the concrete. The objective of this study was to evaluate the effects of preparation parameters, namely, temperature, agitation rate, and pH on the shell thickness and size (diameter) of the microcapsules as well as to evaluate the self-healing mechanism in concrete through experimental testing performed in laboratory. Two healing agents were evaluated in this study, i.e., dicyclopentadiene (DCPD) and sodium silicate. Based on the results of the experimental program, it was determined that, as the pH was increased from 3.0 to 3.7, the shell thickness increased for sodium silicate, while the shell thickness reached a minimum at a pH value of 3.4 for DCPD. Sodium silicate shell thickness was almost twice the shell thickness for DCPD. The most uniform and coherent microcapsules were produced at ...

Evaluation of Interface Shear Strength Properties of Geogrid-Reinforced Construction and Demolition Materials Using a Modified Large-Scale Direct Shear Testing Apparatus

Abstract: The interface shear strength properties of geogrid-reinforced construction and demolition (C&D) aggregates were determined using a modified large scale direct shear test (DST) apparatus. Comparisons were made between the results of the various C&D aggregates reinforced with biaxial and triaxial geogrids and with the unreinforced aggregates by means of the modified and conventional DST methods. The modified DST method employed sought to increase interlocking between the C&D aggregates with the geogrids and thus ascertains the true interface shear strength properties of the recycled demolition aggregates. Biaxial and triaxial geogrids were used as the geogrid-reinforcement materials. The C&D aggregates tested with the DST were recycled concrete aggregate (RCA), crushed brick (CB), and reclaimed asphalt pavement (RAP). The modified DST results indicated that the interface shear strength properties of the geogrid-reinforced C&D aggregates were higher than that of the conventional test method and the r...

Experimental Study on Hybrid Fiber-Reinforced Concrete Subjected to Uniaxial Compression

Abstract: This paper presents the uniaxial compression behavior of steel-polypropylene hybrid fiber–reinforced concrete (HFRC). A total of 30 batches of specimens with different fiber-reinforcement indices in terms of volume fraction and aspect ratio are investigated by the orthogonal experimental method. A variance analysis is conducted to obtain the optimum proportion of hybrid fiber in terms of compressive strength and corresponding peak strain. It is observed from the experimental results that the uniaxial compression behavior of plain concrete can be improved by inclusion of hybrid fibers; it is also noted that the hybrid effect between volume fraction and aspect ratio of steel fiber as well as the volume fraction of polypropylene fiber should be considered as influential factors on uniaxial compressive strength. Furthermore, in comparison to single fiber-reinforced concrete, HFRC exhibits more ductility at postpeak performance. Subsequently, the results are used to develop predictive equations for the...

Durability of Concrete with Recycled Coarse Aggregates: Influence of Superplasticizers

Abstract: The use of recycled aggregates in concrete production can significantly contribute to its sustainability, but it may also jeopardize its durability. The use of superplasticizers may compensate for this performance handicap by contributing to the improvement of the inner structure of this type of concrete. The main goal of this study is to evaluate the effect of standard and high-performance superplasticizers on the key durability-related properties (shrinkage, water absorption by immersion and by capillarity, carbonation and chloride penetration resistance) of concrete made with different percentages of recycled coarse aggregates (RCA) from crushed concrete and compare the findings with the corresponding effect on conventional concrete. The overall conclusion is that recycled aggregate concrete is more susceptible to deterioration because of environmental conditions affecting this concrete’s durability performance more than that of conventional concrete. However, introducing superplasticizers in r...

Research Progresses in Magnesium Phosphate Cement–Based Materials

Abstract: This paper reviews recent studies on preparation, hydration, and properties of magnesium phosphate cement (MPC). MPC is the phosphate-bonded inorganic material derived from reactions between phosphate and magnesium oxide. The hydration reaction in the MgO-NH4H2PO4 system is strongly exothermic, and the main product is struvite (NH4MgPO4·6H2O). The setting time and mechanical properties depend on the proportion and characteristics of raw materials, water to binder ratio, the addition of retarders, and admixtures. Moreover, the MPC demonstrates favorable durability performance compared with Portland cement. Additionally, recommendations for future research are proposed.

Effect of Plant-Induced Calcite Precipitation on the Strength of Sand

Abstract: A plant (jack bean) extract can function as a urease catalyst, similar to those of certain microorganisms such as Sporosarcina pasteurii, which can decompose urea into carbonate and ammonium ions. Carbonate ions decomposed from urea can combine with calcium ions to form calcium carbonate (usually calcite mineral). In this study, calcium chloride, calcium hydroxide, or calcium nitrate was added to urea solution with plant extract, and then mixed with Nakdong River sand to precipitate calcite within the sand-grain matrix. The mixed sand was compacted into a cylindrical specimen and cured for 3 days at room temperature. A specimen without plant extract was prepared for comparison. A series of unconfined compression tests and analytical methods was carried out on sand treated with various amounts of urea and different calcium sources. With increasing amounts of urea, the unconfined compressive strength (UCS) of the sand treated with plant extract increased 10-fold up to 317 kPa, compared to that of th...

Probability Distribution Model for Cross-Sectional Area of Corroded Reinforcing Steel Bars

Abstract: This paper presents the development of a probabilistic model for the cross-sectional area of corroded reinforcing steel bars (rebars), in order to assess the time-dependent reliability of corroded reinforced concrete (RC) structures. The indicator R, which is the ratio of the average to the minimum cross-sectional areas of corroded rebars, was adopted to quantify the longitudinal variation of the cross-sectional area. By using a three-dimensional laser scanning technique, the areas of the discrete cross-sections were evaluated along the length of a rebar at intervals of 1 mm. The statistical results showed that R could be characterized by the Gumbel distribution. Both the location parameter and the scale parameter for the probability distribution of R increased linearly with increases in the corrosion degree and were dependent on the element length and the diameter of the corroded rebar. The results of a time-dependent reliability analysis of corroded RC beams demonstrated that an element length o...

Uniaxial Compressive Strength and Stiffness of Field-Extracted and Laboratory-Constructed Masonry Prisms

Abstract: 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 samp...

Characterizing Rheological Properties of Binder and Blending Efficiency of Asphalt Paving Mixtures Containing RAS through GPC

Abstract: Use of recycled asphalt shingles (RAS) into asphalt mixture has become more popular in asphalt paving industry due to dwindling natural resources and potential economic benefits. However, one critical question arises as to how much of aged asphalt binder in RAS can be effectively blended with virgin binder during mixing and construction. This paper presents a laboratory study in which gel permeation chromatography (GPC) was used to determine the blending efficiency of RAS. A correlation was first established between percentages of large molecules (LMS) obtained from GPC and rheological properties of RAS binders. Then the relationship was used to estimate the blending efficiency of RAS binders. The effects of aggregate size, RAS content, and mixing time on blending efficiency were evaluated. The test results show that the percentage of LMS was highly correlated with the complex shear modulus (G*) of asphalt binder. Increasing mixing time led to a better blending of RAS mixture. Aggregate size did n...

Resilient Modulus and Permanent Deformation Responses of Geogrid-Reinforced Construction and Demolition Materials

Abstract: Extensive amounts of natural quarry aggregates are currently being used in road and pavement applications. The use of construction and demolition (C&D) materials such as recycled concrete aggregate (RCA), crushed brick (CB), and reclaimed asphalt pavement (RAP) as an alternative to quarry aggregates has generated interest in recent years, particularly as a pavement base or subbase material. However, the resilient moduli responses and performance of these C&D materials reinforced with geogrids under repeated loads have yet to be established. This research investigates the resilient moduli (MR) and permanent deformation characteristics of C&D materials reinforced with biaxial and triaxial geogrids with the use of repeated load triaxial (RLT) equipment. The effects of varying deviatoric stress on the resilient modulus of unreinforced and geogrid-reinforced C&D materials were also investigated. Regression analyses of resilient modulus test results were performed using the two- and three-parameter mode...

Empirical Estimation of Pore Size Distribution in Cement, Mortar, and Concrete

Abstract: Pore size distribution is an important factor that affects the moisture diffusion and permeability properties of cement-based materials. For cement paste, it is assumed that the mesopores (100 nm–0.01 mm) and macropores (0.01 mm–1 cm) can be neglected compared to the micropores (<100 nm). Based on the surface energy theory, moisture chemical potential of pore water is introduced to explain the liquid-gas equilibrium in pores with different radius. Using chemical potential as an intermedium, a quantitative relationship between micropore size distribution and water adsorption isotherms can be established. The micropore size distribution can be treated as an explanation of the moisture adsorption behavior, and by using adsorption isotherms, the micropore size distribution can be estimated conveniently. Mortar and concrete can be regarded as a combination of cement paste and aggregates; thus, besides the micropores, the mesopores and macropores are also taken into consideration. Finally, the general ...

Non-Ureolytic Bacterial Carbonate Precipitation as a Surface Treatment Strategy on Cementitious Materials

Abstract: Bacterially induced CaCO3 precipitation is a general phenomenon in nature. It has been proposed as an environmentally friendly strategy for the protection of cementitious materials. This paper investigates the biochemistry of CaCO3 precipitation induced by non-ureolytic bacteria of the genus Bacillus. Different calcium sources are compared for their effectiveness in bacterial mediation of precipitation. Surface treatment using this biodeposition technique is evaluated by parameters affecting the durability of cementitious materials. Outcomes from this study reveal that the type of calcium source has a profound impact on the biochemical process and the crystal form, size, and morphology of bacterially mediated mineralization of CaCO3. An organic calcium source, particularly calcium glutamate, is beneficial for efficient CaCO3 precipitation. Bacterial surface treatment on specimens results in a decrease of more than 50% in capillary water absorption and an increase of nearly 50% in resistance to car...

Accelerated Carbonation of Portland Limestone Cement

Abstract: Accelerated carbonation is a process in which CO2 is intentionally introduced to concrete at an early age for a short period of time to promote rapid strength gain. The accelerated carbonation of portland limestone cement (PLC) was studied to examine the possibility of replacing ordinary portland cement (OPC) by PLC in carbonation curing of precast concrete products. Carbonation behavior was characterized by strength gain, CO2 uptake, pH change, XRD, TG, SEM, FTIR, and Si29 NMR spectroscopy. It was found that PLC was a CO2 reactive material. Its CO2 uptake reached 12% based on dry cement mass. In reference to hydrated PLC, the strength of carbonated PLC was 79% higher at 20 h and of close value at 28 days, even though the ultimate CaCO3 content in carbonated PLC was over 40%. The calcium carbonates produced by accelerated carbonation were found to be imbedded in calcium silicate hydrates, forming an intermingled microstructure. The high carbonation reactivity of PLC was possibly attributed to its ...

Recycled-glass blends in pavement base/subbase applications: Laboratory and field evaluation

Abstract: This paper presents the findings of a field and laboratory evaluation on the use of recycled glass blends as unbound pavement base/subbase materials. The parent recycled aggregates studied in this research were fine recycled glass (FRG), recycled concrete aggregate (RCA), and waste rock (WR). The geotechnical performance of the recycled aggregate blends of particular interest in this research were FRG blended with RCA (FRG/RCA) and FRG blended with WR (FRG/WR) in pavement base applications. The geotechnical performance of a trial road pavement was assessed by means of initial laboratory tests and subsequently field tests. The initial laboratory experimental program included specialized geotechnical tests including repeated load triaxial and triaxial tests to characterize the recycled materials. The subsequent trial road pavement constructed comprised seven different sections of FRG blends in the pavement base varying from 10 to 30% recycled glass content as well as two control sections with RCA an...

Engineering Physical Properties of Asphalt Binders through Nanoclay-asphalt Interactions

Abstract: Increasing traffic volumes, heavier loads, higher tire pressures, and performance problems with asphalt concrete mixtures under adverse conditions are leading state highway departments to using modified binders to enhance the physical properties of asphalt mix. This paper reports the advantages of modified nanoclays (NC) as asphalt modifiers. Dynamic mechanical analysis, flexural creep stiffness, and flexural tests were conducted on the NC-asphalt nanocomposite. In addition, Fourier transform infrared (FTIR) testing was conducted to evaluate the nature of the interactions between NC and asphalt. Increasing NC concentration in asphalt enhances temperature susceptibility of asphalt, as well as increasing the complex modulus in addition to decreasing phase angle. FTIR experiments indicate a significant change in Si─O vibration from NC, indicating strong nonbonded interactions of Si─O tetrahedra with asphalt. These changes in Si─O vibrations suggest both distortion in Si─O tetrahedra as well as strong...

Sulphate Resistance of Geopolymer Concrete Prepared from Blended Waste Fuel Ash

Abstract: The aim of this study is to investigate the performance of geopolymer concrete prepared using blended ash of pulverized fuel ash and palm oil fuel ash from agroindustrial waste along with alkaline activators when exposed to a 5% sodium sulphate solution for up to 18 months. Ordinary portland cement (OPC) concrete was also prepared as the control concrete. The main parameters studied were the evaluation of mass change, compressive strength, products of degradation, and microstructural changes. The deterioration was examined using X-ray diffraction (XRD), a Fourier transform infrared spectroscopy (FTIR), a thermogravimetry analyzer (TGA), and a field emission scanning electron microscope (FESEM). The results of geopolymer and OPC concretes were compared and discussed. The compressive strength of geopolymer concrete, when exposed to a 5% sodium sulphate solution for more than 1 year, was superior to that of OPC concrete. These materials could be used for making sulphate-resistant concretes, attributa...

Mechanical Behaviors of Steel Reinforced ECC or ECC/Concrete Composite Beams under Reversed Cyclic Loading

Abstract: Engineered cementitious composite (ECC) is a class of high performance cementitious composites with pseudo strain hardening behavior and excellent crack control. Substitution of concrete with ECC can avoid the cracking and durability problems associated with brittleness of concrete. In this paper, two series, totaling six steel reinforced beams with various transverse reinforcement ratios, ECC thicknesses, and shear span-depth ratios were tested under reversed cyclic loading. According to the test results, steel reinforced ECC beams show better seismic performance in terms of load carrying capacity, shear resistance, energy dissipation capacity, and damage tolerance compared with steel reinforced concrete beams. The extent of load capacity improvement strongly depended on the failure mode. Beams failed in shear showed more significant improvement than those failed in flexure. For the ECC/concrete composite beam, strategic application of ECC can lead to an increase of energy dissipation capacity. For the steel reinforced ECC beam without stirrups, final failure occurs in shear. However, the ultimate load capacity and deformation are comparable to the steel reinforced concrete beam with properly designed stirrups, and the failure process is ductile due to the strain hardening behavior of ECC materials.

Evaluation of Tensile Strength-Strain Characteristics of Fiber-Reinforced Soil through Laboratory Tests

Abstract: Tension cracking is a very important phenomenon in the case of compacted fine grained soils, which are commonly used in earth dams, embankments, and waste containment systems. The strength and permeability of earthen structures can be seriously affected by the formation of tensile cracks. The purpose of this paper is to evaluate the effect of discrete and randomly distributed fibers (DRDF) in improving the tensile strength-strain characteristics of bentonite amended natural silty soil. The authors conducted a series of direct tensile tests on unreinforced and fiber-reinforced soil by using a specially developed tensile test set up in the laboratory. They conducted tests by varying the fiber content and fiber length and studying their effect on tensile strength-strain characteristics and crack formation. The present paper indicates that the blending of fibers improved the tensile strength-strain characteristics and ductility of the soil. The authors carried out a digital image cross-correlation (DI...

Early Corrosion Detection in Prestressed Concrete Girders Using Acoustic Emission

Abstract: Long-term corrosion tests were performed on prestressed T-girders measuring 498 m (16 ft, 4 in) The test program was composed of four specimens, including one control The specimens were subjected to wet/dry cycles using 3% NaCl solution to accelerate corrosion Two of the specimens were precracked prior to conditioning to examine the effect of crack presence and/or width The specimens were continuously monitored using acoustic emission (AE) Half-cell potential (HCP) measurements and linear polarization resistance (LPR) were performed daily to serve as a benchmark for corrosion detection Acoustic emission can detect the onset of corrosion comparable in time to conventional electrochemical methods Furthermore, AE intensity analysis has the ability to distinguish between different levels of corrosion The specimens were load-tested to measure the residual capacity, which can give an indication of AE’s ability to detect corrosion damage before it affects the strength of prestressed structures

Flexural Behavior of Reinforced Concrete Beams with TRC Tension Zone Cover

Abstract: This research makes a further contribution to the existing knowledge regarding textile-reinforced concrete (TRC) structural members, and the proposed component combines the advantages of TRC and reinforced concrete (RC). This concrete member was experimentally studied and its analytical formulae were derived. Test results of the flexural experiment study indicated that the beams with the TRC layer had some increases in the first crack load, the yield load, and the ultimate moment capacity, compared with the ordinary RC beams, and furthermore the ultimate moment capacity had significant increases with the increase of the reinforcement ratio of textile. A considerable reduction in the crack width and spacing was also observed for the beam with a TRC layer, and thus the postcracking stiffness of the beam was improved. Furthermore, this concrete member has satisfactory flexural ductility. For a single reinforced concrete beam with a rectangular cross section, two types of limit failure states are presented with respect to different reinforcement ratio of textile, and for each state, the relationship between the reinforcement ratio of textile and the reinforcement ratio of steel bar is derived. The calculation methods for the ultimate moment capacity for three failure modes and the midspan deflection during the entire loading process are also presented. A comparison between the calculated and the experimental results reveals a satisfactory agreement and verifies the feasibility of the formulae.

Modeling Mode I Cracking Failure in Asphalt Binder by Using Nonconserved Phase-Field Model

Abstract: 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...

Investigation of the Bond between Concrete Substrate and ECC Overlays

Abstract: Rigid concrete overlays have been used for smoothing damaged surfaces and/or restoring or improving the mechanical capacity of bridge decks for many years. However, engineered cementitious composites (ECCs), which demonstrate superior ductility with high strength and improved durability characteristics, are an attractive alternative to conventional overlay materials if a strong mechanical bond is formed between the overlay and the substrate material. An experimental study was performed to evaluate the bond strength between ECC overlay and an ordinary concrete substrate with smooth and rough surface textures. Microsilica concrete (MSC), generally used as an overlay material, was also prepared as a control mixture. ECC and MSC overlay mixtures were cast over the concrete substrate to determine bonding performance. Slant shear and splitting prism tests were performed with MSC and two ECC mixtures. The experimental results show that when ECC is used as an overlay material, bond strength is significant...

Flexural Behavior of Concrete Beams Reinforced with Different Types of Geogrids

Abstract: This paper describes the behavior of geogrid-reinforced concrete members. The application of geogrids in concrete constitutes a new dimension for using geosynthetics in infrastructure. In pavement applications, geogrids have been used to provide confinement, stabilization, and reinforcement of unbound and asphalt concrete layers, as well as interlayers to mitigate reflective cracking. The ultimate objective of studying the behavior of geogrids in concrete members is to assess the feasibility and benefit of using geogrids in thin concrete overlays. The experimental program consisted of testing 21 simply supported plain and geogrid-reinforced beam specimens under four-point bending. The test parameters included three types of geogrids with different aperture shapes, physical and mechanical properties, and material composition. Additionally, two Portland cement concrete mixtures were used: normal and high strength. Results from testing confirm the reinforcing benefit of the geogrids as evidenced from the load-deflection response in terms of postpeak behavior, load capacity, crack mouth opening displacement (CMOD), and failure mode. Conclusions regarding correlations between the failure properties and the properties of the geogrid are made.