Journal of Materials in Civil Engineering

In this paper, the plastic settlement of mortar is analyzed on the basis of small strain consolidation theory and the approach is compared with experimental data. The amount of settlement caused by the self-weight of bulk mortar was measured using a noncontact laser measurement device. In addition, tests were performed on systems containing different geometries of embedded reinforcement to measure the effect of specimen and inclusion geometry on settlement. The influence of mixture proportions and cover depth were analyzed. The experimental results were correlated with results from the numerical simulation of fresh mortars using consolidation analysis. The results suggest that consolidation theory can be used as a reasonable approach to analyze plastic settlement. Further, this model can be used to demonstrate the effects of differential settlement over reinforcing bars or changes in section height.

The presence of air voids, moisture, and chlorides inside tendon systems on segmental posttensioned (PT) bridges has been cited as a reason for the early age corrosion and failure of strands in these bridges. This paper develops probabilistic models to predict the time-variant tension capacity of PT strands exposed to wet-dry conditions. A total of 384 unstressed and 162 stressed strand test specimens were exposed to various void, moisture, and chloride conditions for 0, 12, 16, and 21 months; the residual tension capacities of the strands were then determined. Using these experimental data, a Bayesian approach is used to develop probabilistic capacity models for unstressed and stressed strands. The tension capacities of stressed strands under potential void, wet-dry, and chloride conditions in the field are predicted using the developed models. Probabilistic time-variant models are formulated in such a way that they can be updated by other researchers using additional information from the testing of unstressed strands only, avoiding expensive and cumbersome testing of stressed strands. The mean absolute percentage errors of these models are less than 3.2%, indicating good overall model accuracy.

The failures of the bituminous pavements are not only due to increase in traffic but also due to extreme climatic conditions prevailing in the country. There are very high and very low pavement temperatures that exist during different seasons of the year. Thus, climatic conditions play an important role in selecting the type of materials to be used in road construction. In order to increase the life of bituminous pavement, quality of bitumen needs to be enhanced. To achieve the improvement of binder, it is necessary to add the polymers to bitumen. In this study, two types of polymer — ethylene vinyle acetate (EVA), a plastomer, and linear styrene-butadiene-styrene (SBS), an elastomer — and crumb rubber (CR) were used. The changes of rheological properties of 60/70 grades bitumen modified with different percentages of CR, EVA, and SBS (3–9%) were studied. The rheological properties of the bituminous binders in terms of their complex modulus $\left(G^{\ast }\right)$ , stiffness and overall resistance to deformation, storage modulus $\left(G^{\prime }\right)$ , binder elasticity, loss modulus $\left(G^{″}\right)$ , viscous behavior and phase angle $\left(\delta \right)$ , and viscoelastic behavior were measured by using dynamic shear rheometer (SR5 asphalt rheometer). Testing was performed at higher temperatures ranging from 46 to $82°\text{C}$ in increments of $6°\text{C}$ at a frequency of 10 rad/s in the range from 0.1 to 100 rad/s before and after aging. It was observed that the rheological properties of bituminous binders had changed after modification. There is an improvement in rheological properties of the neat bitumen after mixing with modifiers.

The mixing moisture content (MMC) is an important mix design variable in pavement full-depth reclamation (FDR) with foamed asphalt. It has been known for many decades that MMC in the granular material subjected to foamed asphalt treatment can affect asphalt dispersion. This paper investigates the micromechanics of this phenomenon by combining direct microstructure observations and conventional laboratory testing. It was found that for a typical loose moist granular material with a considerable amount of fine particles, the agglomeration state evolves through a series of states as the MMC increases. If the MMC is high, the fine particles become saturated and form a pastelike substance that coats larger aggregate particles, creating large agglomerations with low surface area to volume ratios. Inferior asphalt dispersion is resulted for mixes in this state. Theories for wet agglomeration processes are used to explain the observations on the basis of thermodynamic equilibrium. Fracture face image analysis for tested indirect tensile strength specimens confirmed this observation. Laboratory tests also found that mixes with inferior asphalt dispersion due to suboptimal MMC yield low strength and low stiffness. These effects are particularly significant for granular materials with higher fines content. The main practical implication of the findings is that relatively dry loose granular mixes are preferred for foamed asphalt dispersion, and a balance should be sought between asphalt dispersion and mix compactability. The existing postulation that high MMC aids foamed asphalt dispersion is therefore dismissed.

To understand the behavior of hot-poured bituminous-based crack sealants at low service temperatures and to predict their field performance, a constitutive stress-strain relationship must be described. This would allow predicting in situ crack sealant response to both thermal and traffic loading. This paper verifies the linear viscoelastic behavior of crack sealants. Ten sealants having high polymer contents were tested at −4 to $-40°\text{C}$ using a Crack Sealant Bending Beam Rheometer (CSBBR). The convolution integral principle was used to obtain relaxation moduli from measured creep compliance data. A Prony series viscoelastic model was used to characterize mechanical behavior of crack sealant at low temperatures. The sealant’s linear response was checked by implementing two conditions of linearity described by Marasteanu and Anderson. Simulation for the sealant linear viscoelastic deflection response during the loading and unloading was conducted using a three-dimensional finite-element model. This study concludes that mechanical behavior of crack sealants may be accurately described by a linear viscoelastic model at low service temperatures.

Self-compacting concrete (SCC) is being used in high-rise buildings and industrial structures which may be subjected to high temperatures during operation or in case of an accidental fire. The proper understanding of the effects of elevated temperatures on the properties of SCC is necessary. This paper reports the results of laboratory investigations carried out to study the effects of high temperatures ranging from room temperature to $800°\text{C}$ on the compressive strength of different water-cement ratio SCC and high-strength concrete. It is found that the hot compressive strength of SCC decreases with increasing temperature. Compared with normal-strength SCC, high-strength SCC possesses a larger compressive strength exposed to high temperature. Another result of tests is that addition of polypropylene fibers decreased the strength and probability of explosive spalling.

The effect of polypropylene application method on long-term aging of hot mix asphalt (HMA) was investigated. Three different application methods were considered within this paper, namely, the coating method (where aggregate surface was coated with polypropylene), the dry method, and the wet method. Constant polypropylene content of 0.7% by weight of total mix was adapted. Laboratory aging program was set up to simulate the aging process of asphalt pavement occurred in the field. The mechanical properties of aged and unaged mixtures prepared using the three different polypropylene application methods were evaluated based on Marshall quotient, the indirect tensile strength, fracture energy, and unconfined compressive strength. Experimental testing has revealed the enhancement in the mechanical properties of HMA when polypropylene was added. The polypropylene additive has managed to counteract the effect caused by long-term aging of HMA. A comparison between the three polypropylene application methods indicated that the coating method has caused a considerable improvement in the indirect tensile strength and fracture energy of HMA under aged and unaged conditions. Marshall quotient and compressive strength of tested mixtures have shown less dependency on the polypropylene application method.

This research used laboratory evaluations to study the effect of using low-density polyethylene (LDPE) additive on the fracture toughness of asphalt concrete mixtures. LDPE was mixed with asphalt at $160°\text{C}$ and incorporated into the mixture. LDPE content of 1.5, 3, and 4.5% by total weight of asphalt was adapted. Fracture toughness evaluation was based on the J-integral concept. Innovative semicircular specimen geometry (76-mm radius and 57-mm thickness) is employed in fracture toughness evaluation. Notches with different depth-to-radius ratios were introduced at the middle of the flat surface of each specimen. Three-point bend loading was used to allow the separation of the two surfaces as a result of tensile stresses at the crack tip. Application of the J-integral concept revealed the fracture toughness superiority of the LDPE-modified asphalt concrete mixtures as compared to the unmodified mixture. The fracture toughness is sensitive to the LDPE concentration. Mixtures modified with 4.5% LDPE experienced the highest fracture toughness. LDPE modification has also enhanced the physical properties of asphalt cement. The LDPE-modified asphalt concrete mix displayed a significant increase in both indirect tensile and compressive strength.

The production of self-compacting concrete (SCC) is a relatively new technology. Nowadays, the production of SCC is becoming more popular in Turkey owing to its superior properties. However, the production of SCC requires more sensitive and efficient workmanship and equipment. In addition to many other factors, such as proportioning and curing, the origin of coarse aggregate and mineral admixtures carries utmost importance in terms of fresh and mechanical properties of SCC. The effect of two mineral admixtures—fly ash and limestone powder—and two types of coarse aggregates—limestone and olivine basalt—on fresh and hardened SCC have been investigated within a series of laboratory tests. Results showed that the effect of mineral admixtures on fresh properties seems to be more dominant than the effect of aggregate type. Limestone powder and limestone aggregate combinations had superior fresh and mechanical properties compared to basalt-incorporated mixtures.

The study of using palm oil fuel ash (POFA) in concrete work is just the beginning, and obtained data are very little as compared to fly ash and silica fume. In order to collect experimental data, the effects of ground POFA (GPOFA) replacement rate up to 30 wt % and water/binder (W/B) ratios of 0.50, 0.55, and 0.60 on normal concrete properties were studied. GPOFA with high fineness was found to be a possible pozzolanic material in concrete. Cement replacement of GPOFA at rates of 10 and 20% yielded higher compressive strength than that of control concrete after 28 days of curing. In addition, heat evolution in terms of temperature rise of fresh concrete decreased with an increased of GPOFA replacement. For concrete with a W/B ratio of 0.50, the use of 30% GPOFA as a cement replacement exhibited the lowest peak temperature rise. However, a decrease compressive strength at early age might be considered if a high replacement rate of GPOFA was used.

Thermoviscoelastic properties and creep response of two commercial ambient temperature cure epoxy structural adhesives were analyzed and compared. The adhesives were formulated by the same manufacturer and appeared to be chemically similar; however, one system contained accelerators to shorten its cure time. In the laboratory, dynamic mechanical temperature/frequency sweeps were performed on both systems to generate dynamic mechanical and creep compliance master curves using time-temperature superposition principles. Differences were observed in the dynamic mechanical properties of the two adhesive systems as well as in their calculated creep compliance, which have been attributed to differences in their curing agent(s) and accelerator(s). Full-scale creep tests were carried out on anchors installed in concrete slabs and subjected to sustained loads for 82 days. These results were in good agreement with the creep compliance estimated using time-temperature superposition, suggesting that dynamic mechanical testing can be a useful metrology for characterizing trends in creep behavior.

Rising energy prices, global warming, and more stringent environmental regulations have resulted in an interest in warm mix asphalt (WMA) technologies as a means to decrease the energy consumption and emissions associated with conventional hot mix asphalt production. However, the utilization of the hydrated lime and liquid antistripping agents (ASA) in WMA mixture makes these issues more complicated. The objective of this study was to investigate and evaluate the moisture susceptibility of the mixtures containing ASA and WMA additives. The experimental design for this study included the utilizations of one binder source (PG 64-22), three ASA additives and control, two WMA additives and virgin, and three aggregate sources. A total of 36 types of mixtures and 216 specimens were fabricated and tested in this study. The performed properties include indirect tensile strength (ITS), tensile strength ratio (TSR), flow, and toughness. The results indicated that the hydrate lime exhibits the best moisture resistance for WMA mixtures, the liquid ASA additives can increase the ITS values of the mixtures but the liquid ASA generally exhibits a weak moisture resistance compared to the hydrate lime regardless of WMA and aggregate types in this study. In addition, the wet ITS values of mixtures containing WMA additives were lower than that of the mixtures without WMA additives.

This paper introduces a newly developed steel-fiber-reinforced polymer (FRP) composite bar (SFCB) and proposes the ideal configuration based on a large number of exploratory tests on handmade products. Based on factory production of SFCB, uniaxial tensile tests and cyclic tensile tests were conducted to determine the initial elastic modulus, postyield stiffness, yield strength, ultimate strength, unloading stiffness, and residual deformation. Test results showed that the stress-strain curve of the SFCB was bilinear before the fiber fractures. After the inner steel yielded, the SFCB showed a stable postyield stiffness, small residual deformation, and good reparability. Because the theoretical model for the stress-strain curve of SFCB under a uniaxial load based on the mixture rule had large error with data from cyclic tests, the corresponding restoring force model under cyclic tensile loading was constructed by statistical analysis of the stress-strain test curve under cyclic tension. The generated restoring force model accurately displayed the trend of unloading stiffness of SFCB degradation with cyclic loads. Furthermore, the predicted results were in good agreement with the experimental results, which proved that the mechanical properties of SFCB could be predicted and designed by the proposed model.

Ultrahigh toughness cementitious composite (UHTCC) is a new class of high performance fiber-reinforced cementitious composites which exhibits pseudostrain hardening and multiple cracking phenomena. The main objectives of this paper are to investigate the compressive properties of UHTCC and to develop the constitutive models to describe it. The complete study includes an experimental phase and an analytical phase. In the experimental phase, the stress-strain curves were directly obtained, and the compressive parameters, i.e., strength, average strain at maximum stress, elastic modulus, and Poisson’s ratio, were calculated. The relationships of compressive parameters as a function of compressive strength were proposed according to the test results. The comparisons between UHTCC and matrix were carried out to understand the fiber effect on the compressive parameters. In the theoretical phase, comparisons were conducted between experimental results and existing models. As a result, two analytical relationships were proposed for design purpose under ultimate limit state conditions and nonlinear analysis of UHTCC structures. The research should lead to better understand the compressive properties of UHTCC and the mechanisms of fiber reinforcement for UHTCC and to provide analysis models for design or analysis of UHTCC structural members.

Large amounts of rice husk ash (RHA) are produced every year worldwide, and difficulties related to its disposal may cause this product to become an environmental hazard. Owing to its high amorphous silica content, RHA has shown to be a valid supplementary cementing material in the production of concrete. This paper presents the physical and chemical properties of a new generation RHA that is off-white in color, is carbon neutral, and has no crystalline ${\text{SiO}}_2$ and toxic metals. The effects on mechanical properties of a mixture using off-white rice hull ash (OWRHA) as partial replacement of white cement were also investigated. The OWRHA-blended concrete has higher compressive and splitting tensile strengths at various ages compared with the control mixture. It is shown that up to 15% of OWRHA could be advantageously blended with white cement to enhance white concrete performance without modifying the aesthetics of the final product.