Journal of Materials in Civil Engineering

The objective of this paper is to verify the time-temperature superposition (t-TS) principle for hot-mix asphalt (HMA) with growing damage and permanent strain at different confining pressures in both the tension and compression stress states. Dynamic modulus tests at various confining pressures were conducted both in tension compression and in compression. The results were investigated to evaluate the effects of confining pressure and stress on the thermorheological simplicity of HMA within the linear viscoelastic range. Constant crosshead rate tests, both in tension and in compression, and repetitive creep and recovery tests in compression were also performed to check the t-TS principle with growing damage and permanent strain level with regard to the effects of confining pressure and stress. The analysis results show that the HMA remains thermorheologically simple regardless of stress state, damage, and permanent strain level under the same confining pressure. However, confining pressure does have an effect on the dynamic modulus and shift factor, especially at a high temperature and/or low reduced frequency.

Fire is one of the most severe conditions to which structures can be subjected, and hence, the provision of appropriate fire safety measures for structural members is an important aspect of design. The recent introduction of performance-based codes has increased the use of computer-based models for fire resistance assessment. For evaluating the fire resistance of steel structures, high-temperature properties of steel are to be specified as input data. This paper reviews high-temperature constitutive relationships for steel currently available in American and European standards, and highlights the variation between these relationships through comparison with published experimental results. The effect of various constitutive models on overall fire resistance predictions is illustrated through case studies. It is also shown that high-temperature creep, which is not often included in constitutive models, has a significant influence on the fire response of steel structures. Results from the case studies are used to draw recommendations on the use of appropriate constitutive models for fire resistance assessment.

Particle size of the fly ash governs its utilization in various engineering projects. This could be obtained by either conducting dry- and wet-sieving or hydrometer analysis. Though, for a material with a particle size less than $75\mu \text{m}$ , the hydrometer analysis is best suited, difficulties associated with it are well known. This necessitates application of advanced techniques such as laser particle analysis, soft imaging, etc. However, not only are these techniques cost intensive, but they also fail to yield reliable results, particularly, if the material is heterogeneous and the particles are coarser. This calls for resorting to dry or wet sieving for accurate determination of particle-size distribution characteristics. However, not many studies have been conducted that critically evaluate and compare the results obtained from these methodologies in relation to those obtained from the hydrometer tests. With this in view, investigations were conducted on different fly ashes by conducting dry sieving. In addition, the fraction of fly ash retained on $45\mu \text{m}$ sieve was determined by employing wet sieving. Results obtained from these methodologies are critically examined. It has been demonstrated that dry-sieving with plastic balls yields reliable results in less time as compared to the wet sieving and hence this methodology would be better suited for pozzolanic materials.

Motivations for adopting recycled concrete as an aggregate source include the preservation of natural resources, effective utilization of a growing waste stream, and financial and energy savings. Although current New Zealand practices include some use of crushed concrete in road construction, use of recycled concrete aggregate (RCA) in low specification concrete is currently infrequent and the use of recycled concrete as an aggregate source in structural concrete applications is rare. To make such recycling feasible, the properties of RCA must be related to the properties of new concrete that utilizes the recycled aggregates. In response to this need, a study was undertaken to investigate the feasibility of using RCA as a viable alternative to natural aggregate (NA) in the production of concrete manufactured in a conventional New Zealand ready mix concrete plant. Aggregate properties and hardened and fresh concrete properties of RCA concrete were studied and compared with the associated properties derived from NA concrete. Results indicated that RCA is a viable alternative to NA in the production of concrete. Furthermore, it was confirmed that the properties of RCA dictate the hardened properties of the reconstituted concrete and that RCA from certain strength placements limited the resulting possible strengths of concrete produced from it.

This paper discusses a laboratory study used to characterize bituminous binders based on their dynamic creep resistance. Laboratory testing using four different loading regimes on asphalt mixes with six different bituminous binders was undertaken. Creep cycles to 2% accumulated strain were used to define the creep resistance of the asphalt mixes with the various binders. Underlying viscosities of the bitumens were derived using the Australian Road Research Board (ARRB) Elastometer. Marshall stability was measured on the specimens that were prepared using gyratory compaction. Regression plots were prepared that link creep resistance, underlying viscosity, and Marshall stability. It was found that the ARRB Elastometer is able to measure underlying viscosity, which is a reasonable predictor of dynamic creep resistance. Marshall stability was also shown to be a good indicator of dynamic creep resistance. Therefore, simpler tests such as Marshall stability and Elastometer can be used to rank bituminous materials for asphalt mix design purposes in the laboratory.

This paper presents an experimental study on flexural testing of three different types of soils molded at three different water contents and two different compaction energies. For this purpose, a custom designed simple beam test setup was developed in the laboratory for inducing the controlled pure bending to the soil under evaluation together with a charged coupled device video camera mounted on to a moving triaxial base plate. Based on the analysis and interpretation of bending moment (BM)-curvature $\left(\kappa \right)$ relationships of tested soil beams, effects of soil type, molding water content, and compaction energy on the flexural behavior could be obtained. For the varied molding water contents and for the range of plasticity indices varied, with an increase in plasticity index of the soil and molding water content, a trend of increasing tensile strain at crack initiation was observed. In comparison, flexural tensile strength at crack initiation was observed to decrease with an increase in molding water content. Further, flexural rigidity at crack initiation was found to be higher for soils having low plasticity index and moist compacted at low-molding water contents. The developed test setup is capable of inducing distortion levels of 0.105 and can be useful in assessing flexural characteristics of different types of fine-grained soils.

Pervious concrete is becoming more common as a storm-water management tool in freeze-thaw climates. One of the main concerns or obstacles preventing a more widespread application is the aspect of freeze-thaw durability, whether perceived or actual. This paper describes a series of tests designed to determine the specific role coarse aggregate has on the freeze-thaw durability of pervious concrete using the ASTM C666A procedure. 17 different coarse aggregate samples were obtained from locations across the United States and Canada. Pervious concrete mixtures were placed using a mixture proportion previously determined as freeze-thaw durable. The range of durable aggregate gradations clearly defined a gradation specification and suggestions are made for optimizing the gradation with a small portion of sand. Mixtures with excellent freeze-thaw performance contained either granite or highly durable river gravel. The impact of aggregate angularity on mixture proportions and ultimate yield is also discussed.

This research explains an experimental investigation of the concrete applying nonlinear ultrasonic testing technique. Eighteen cubic specimens, $150\times 150\times 150\text{mm}$ , were prepared from three concrete batches with w/c of 40, 50, and 60%, respectively. The hardened concrete specimens after 28-day of curing were simultaneously subjected to uniaxial compression and nonlinear ultrasonic testing. The specimens were damaged by gradually loading them in compression in several steps representing 0, 20, 40, 60, and 80%, respectively, of the specimen’s ultimate strength. At the end of each loading step ultrasonic evaluation was performed and the time domain waveforms were recorded at different power levels. Fast Fourier transformation (FFT) of the time domain waveforms was conducted to produce the frequency spectra. The data obtained from frequency spectra was used to study the change in signal amplitude or signal attenuation. It was found that attenuation is quite sensitive to different damage and power levels. The Fourier amplitudes obtained from FFT of the time domain data were normalized at fundamental frequency. Normalized spectra were used to examine the generation of second harmonic wave components. It was also found that the formation of second harmonic components are highly sensitive to increase in damage and change in power levels.

In the mechanistic-empirical pavement design guide, prediction of flexible pavement response and performance needs an input of dynamic modulus of hot-mix asphalt at all three levels of hierarchical inputs. This study was intended to find the best way to predict/derive this input. Nine Superpave pavement sections were selected as test sections in this study. Deflection data on all test sections was collected with a Dynatest 8000 falling weight deflectometer shortly after construction. The deflection data, normalized with respect to 40-kN load, were used to back-calculate asphalt layer moduli using three back-calculation algorithms. Laboratory dynamic modulus tests were conducted on asphalt concrete (AC) cores and laboratory-compacted samples. Dynamic modulus was also estimated with the Witczak model, new Witczak model, and Hirsch model. The results show that the AC moduli obtained from various back-calculation programs used in the study are generally comparable. Laboratory dynamic modulus is comparable at $4°\text{C}$ , but the variation increases as the test temperature increases. The Witczak model underestimates the dynamic modulus at low temperature and overestimates it at higher temperature. The parameter estimate when the laboratory dynamic modulus is used as a dependent variable and the moduli from other approaches as independent variables is close to 1. This is especially true for the AC moduli estimated by various prediction methods. The Hirsch model appears to be the best for estimation and is closely followed by the new Witczak model.

This paper presents the findings of a laboratory investigation on the characterization of a freshly quarried granular base material lightly stabilized with slag-lime cementitious binder involving unconfined compression (UC) testing and indirect diametrical tensile (IDT) testing, both with internal displacement measurements. The UC test investigation involved the determination of the unconfined compressive strength (UCS) and four different types of stiffness moduli from both internal and external displacement measurements. The IDT testing included the determination of IDT strength as well as the static and dynamic stiffness moduli (i.e., SSM and DSM) of the lightly stabilized granular base material from monotonic and cyclic load IDT testing. This study indicates that the stiffness moduli of a lightly cementitiously stabilized granular base material can be determined consistently from UC testing by measuring the deformations internally, and the modulus is more reliably defined as either the tangent modulus at half the ultimate stress or secant modulus at 0.02% strain. The UC stiffness modulus could be estimated reliably from the corresponding UCS value using the regression relationships established from this study. The IDT strength was determined to be equal to 0.1143 times the UCS value and this conforms to the recommendation given in design guides such as AUSTROADS. Moreover, the IDT, DSM, and SSM of a lightly cementitiously stabilized granular base material could be estimated from the UCS of the same material using the correlations developed in this paper which could be used in pavement design.

This study examined the effects of two freeze-thaw (FT) laboratory procedures, FT-1 and FT-2, on stabilized aggregate specimens. Cylindrical specimens were stabilized with 10% Class C fly ash (CFA) cured for selected periods and then subjected to either FT-1 or FT-2 cycles. FT-1 and FT-2 procedures consisted of freezing specimens at $-25°\text{C}$ for 24 h and thawing them at $21.7°\text{C}$ for another 24 h with a high relative humidity; the only difference was that FT-1 required a membrane around each specimen, while FT-2 required no membranes during freezing and thawing. After being subject to freezing and thawing actions, specimens were then tested for resilient modulus $\left(M_R\right)$ and unconfined compressive strength (UCS) values. Results showed that the $M_R$ values of 28-day cured specimens increased as FT-1 cycles increased up to 12, beyond which a reduction in $M_R$ values was observed. For 3-day cured specimens the $M_R$ increased with FT-1 cycles up to 30. The UCS values of 28- and 3-day stabilized specimens also exhibited the same trend as the $M_R$ with FT-1 cycles. In addition, the specimens subject to 30 FT-2 cycles exhibited a higher reduction in $M_R$ values than the specimens subject to FT-1. This behavior is explained by the moisture increase in the specimens subject to FT-2 cycles which caused an ice lens formation in the fine matrix and destruction in the particle matrix. The study also showed that the $M_R$ -stress model recommended by the new mechanistic-empirical pavement design guide for unbound pavement materials could be a statistically good and a reliable predictor of the $M_R$ values of stabilized aggregate bases.

Autogenous healing can occur when hairline cracks in concrete repair themselves through reactions with water and/or constituents in water. The chemistry of water contacting the cement affects whether the crack heals autogenously or propagates until leaks occur. The strength testing on concrete specimens demonstrates that appreciable healing can occur at a pH of 9.5 when there is sufficient magnesium and silicon in the water. Scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) analyses indicate that a magnesium silicate material is present within the crack surfaces when higher strength healing has occurred. Calcium does not appear to promote the sealing of cracks. A carbonation of internal concrete surfaces was not detected when cracks were sealed via autogenous healing. Chloride diffusion rates do not return to levels seen in virgin concrete when cracks are autogenously healed. However, the water permeability and chloride diffusion are impeded by any filling of cracks regardless of the strength attained.

The effects of pore structure of concrete made with slag-blended cement on shrinkage behavior of concrete when exposed to drying were presented in this paper. The investigated parameters were the length of curing (1-day and 7-day curing), slag and gypsum contents in mixtures. Pore structure analysis was studied by conducting mercury intrusion porosimetry and nitrogen gas adsorption technique tests. The results show that 65% slag concrete with 7-day curing exhibited the lowest shrinkage evolution compared to 0, 35, 50% slag mixes. This is attributed to the highest pore radius where meniscus forms when drying in these concretes. It was found that addition of gypsum in slag mixes tend to reduce the nanopores (within the range from 4 to 20 nm pore size) and decrease the proportion of mesopores. The higher proportion of mesopores and the lower value of meniscus pore radius could explain the increase in drying shrinkage of concrete made with 65% slag cement containing 0% added gypsum.

The paper brings out the influence of relative density of foundation soil on performance improvement of geocell reinforcement; through model load tests on geocell-reinforced and unreinforced sand beds. Tests were carried out for five different relative densities of sand (30, 40, 50, 60, and 70%). The test results indicate that the beneficial effect of geocell reinforcement, in terms of increase in stiffness, bearing capacity, and load dispersion angle of the foundation bed, is present over a wide range of relative density; however, it is higher for dense condition of foundation soil. With geocell reinforcement offering three-dimensional confinement, the dilation induced benefit is substantially high for dense soil fill. Therefore, for effective utilization of geocell reinforcement, the foundation soil should be compacted to higher density.

A composite geomaterial (CGM) is developed using dredged soil, bottom ash, cement and air foam. The engineering properties of the CGM are characterized as a function of the content of the various admixtures and the curing time in a laboratory test program. Several series of unconfined compression tests were carried out to characterize the strength and elastic properties of the CGM. Experimental results indicate that the unconfined compressive strength and modulus of CGM are influenced by the content of each component in the mixture. The unconfined compressive strength of CGM increases with an increase in curing time due to the pozzolanic reaction of the bottom ash. The strength after 28 days of curing is found to be approximately 1.5–2.3 times the strength after 7 days of curing, regardless of mix conditions. The bottom ash materials contain nearly 50% siliceous material and 13.9% CaO. With the removal of particles larger than 4.75 mm, a larger surface area is available to react with cement. It is postulated that the increase in shear strength is caused not only by the development of friction at the interface of the mixture components, but also by bond strength is due to the pozzolanic reaction of the bottom ash. Further study is needed, however, to discern aspects related to increase in pozzolanic reaction of bottom ash with the removal of larger size particles. The secant modulus of CGM is in the range of 185–480 times the unconfined compressive strength. The observed general trend is that the stiffness of CGM is greater than that of lightweight soil not containing the bottom ash as a component.