Journal of Materials in Civil Engineering

The moisture content in the concrete pores is a critical parameter for most of the degradation processes suffered by concrete, for example concrete shrinkage and related cracking. In the present paper, the development of internal relative humidity of a concrete slab at an early age was investigated by applying the temperature and humidity combined digital sensor. The experimental results show that the internal relative humidity of concrete is reduced with concrete age. The general law of the development of relative humidity inside of concrete can be described by a vapor-saturated stage with 100% relative humidity (Stage I) followed by a stage that the relative humidity gradually reduced (Stage II). The length of Stage I and the magnitude of relative humidity in Stage II are greatly influenced by the strength of concrete and the location in concrete. A humidity gradient along the thickness of the concrete specimen existed at an early age. The humidity gradient in high-strength concrete (C80) is more obvious than that in normal-strength concrete (C40). In addition, for a given age, the reduction in relative humidity in C80 is much higher than that in C40.

Artificial aggregates produced from mine waste geopolymeric binders were studied as a potential substrate for fixed-film wastewater-treatment processes (biofilm reactors). Waste geopolymeric artificial aggregates (WGA) of 2–3 cm in size were produced using geopolymeric mine waste mud as a precursor and both sodium silicate and sodium hydroxide as alkaline activators. Seven mixtures were produced with different atomic ratios of sodium silicate to sodium hydroxide (S/H) and of precursor (waste mud) to sodium silicate (P/S), using curing temperatures of 20°C and 130°C, for a total of 112 samples. Structural stability and pH variation after immersion in water were observed over an 18-week period. The results showed that the initial water pH decreased with the increase of the curing time, taking between 17 and 42 days to reach pH 8. The mixture cured at 20°C for 28 days appears to be suitable for use as a substrate for biofilm reactors because the initial water pH was one of the lowest (approximately pH 10), and the time necessary to stabilize it to approximately pH 8 was only 17 days.

The purpose of the study was to propose accurate models for predicting bending strength that are valid for a wide range of beam qualities. For the study, 26 European oaks (Quercus robur L.) were felled in northwestern Spain, where most of the oak stands in the country are located. The trees were sawn, and a sample of quarter-sawn planks was selected. Planed and edged specimens ($5\times 10\times 200\mathrm{cm}$) were tested to obtain the modulus of rupture (MOR) in axial direction bending, the modulus of elasticity (MOE), density, moisture content, and size of defects. The MOR was correlated with the MOE and with maximum edge knot diameter. The correlation was not high enough to justify construction of a predictive model of mechanical behavior on the basis of maximum knot size in the piece. The analyses enabled development of a model for predicting MOR, with MOE as the only predictor variable ($R^2=0.65$; $\mathrm{\text{bias}}=0.6\%$).

The mechanical property of timber is a prerequisite for the evaluation of ancient timber structures. The main mechanical properties of three kinds of timber including the old Tibetan Populus cathayana, new Tibetan Populus cathayana and new Tibetan Pine were obtained by tests in this paper. The principles and assumptions made in the determination of these strengths and the time-dependent laws on the design strength of timber in ancient Tibetan structures were discussed. It is found that the physical and mechanical properties of Tibetan Populus cathayana have degraded greatly after hundreds of years. The strength degradation of a structural component can be attributed to the decay and cracking of timber when the stress ratio is low while it can be attributed to the creep of timber caused by the load duration effect when the stress ratio is high. The new Tibetan Pine is also checked to be a good material for the restoration of ancient Tibetan building due to its higher strength compared to the old Populus timber.

Backfilling and injection of granular materials into mining induced voids, separated beddings, and cracks, as either diluted slurry or concrete paste, is widely used to control coal mine subsidence. As a viable environmental solution, mine waste and rejected materials from underground coal seams are used in both backfilling and injection mine operations. During longwall mining, the grout slurry is pumped into the separated beds of the fractured rock mass through a pipeline connected to a central vertical borehole, which is drilled deep into the interburden rock strata above the coal seam. Either as dilute slurry or thick paste or cake, the fill material normally needs to travel a significant distance in a long pipeline. A blockage can occur in the pipeline when the slurry velocity falls below a certain critical threshold value, indicating a material phase change from cohesive-viscous to cohesive-frictional. In a previous study of radial flow through disks, complete analytical solutions of the required pump pressure versus fluid volume rate were presented for such slurries, categorized as frictional Bingham-Herschel-Bulkley fluids. This paper is an extension to the theory of fluid mechanics to this type of flow in uniform circular pipes. General analytical solutions were developed for complex fluids in velocity and pressure gradients and velocity and pressure as a function of pipe length, from which special and familiar equations for simpler fluids are derivable by mathematical reduction of the general equations. This study differs from the previous research in consideration of the variable shear parameters rather than fixed values, inclusion of total nonlinear behavior, and implementation of a friction function to mimic behavior of the depositing and consolidating stiff slurry, which can cause a significant pressure rise as a result of the increased shear resistance.

Dispersion of carbon nanotubes (CNTs)/carbon nanofibers (CNFs) in cement matrixes is one of the key problems for fabricating piezoresistive CNT/CNF cementitious composites. The use of existing dispersants such as sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (NaDDBS), and methylcellulose to disperse CNTs/CNFs has negative effects on the hydration of cement and will cause decreases in the mechanical properties of cementitious composites. In this study, a superplasticizer, a commonly used component in cementitious composites, is found to be capable of effectively dispersing CNTs and CNFs in a cement matrix. This eliminates the need for additional dispersants for fabricating piezoresistive CNT/CNF cementitious composites and avoids the impairment of composite properties by additional dispersants. The dispersion of CNTs/CNFs in cement matrix is evaluated by observing the dispersion of CNTs/CNFs in the superplasticizer aqueous solution, examining the morphology of composites, and analyzing the discreteness of resistance of composites. The piezoresistive responses of the composites with different types and concentrations of CNTs and CNFs are also investigated. Experimental results show that the fabricated CNT/CNF cementitious composites have strong piezoresistive responses, and the piezoresistive response sensitivity depends heavily on the types and concentrations of CNTs and CNFs. These findings indicate that piezoresistive CNT/CNF cementitious composites can be developed only by using a typical component of cementitious materials (i.e., superplasticizer) as dispersant and without adding any additional dispersants for CNTs/CNFs.

Two investigative stages are presented in this study, which aim to establish basic standards for the use of calcined paper sludge (CPS) in the stabilization of soils. The soils were stabilized with CPS and with mixtures of CPS and cement ($\mathrm{C}$). The total percentage of binder was between 3 and 6% by weight. The blending ratios (by weight) of the CPS:C mixtures were $50:50$ and $25:75$. The first stage took place in the laboratory, and the second stage, in the field, involved in situ stabilization of 250 m of subgrade using dry-mix methods. The bearing capacity of the stabilized soils was determined in the laboratory. In the second stage, the densities of the subgrade were measured in the field following compaction and deflections at 7 days. Furthermore, the evolution of its unconfined compressive strength (UCS) was measured over 90 days. The results reveal optimal mechanical behavior of the stabilized soil at CPS:C ratios of approximately $25:75$.

Foam-based Warm Mix Asphalt (WMA) technologies decrease the viscosity of the asphalt so that it is workable during construction. However, after construction, viscosity increases rapidly as the foam disappears and temperature drops. During the process of dissipation of foam, depending on the environmental conditions, the moisture may not escape and may be trapped inside the mixture. This trapped moisture can cause detrimental failures by breaking the adhesive bonds between the aggregates and the asphalt binder (because of diffusion and freeze/thaw cycles). It is crucial to know how the moisture escapes from the asphalt mixture as the specimen cools down and foam disappears. In this research, dissipation of the moisture from foamed asphalt binders was directly measured and quantified by using a high-resolution synchrotron-based X-Ray Microtomography (XRM) system. Different foamed asphalt binders were instantly frozen by using liquid nitrogen at different times after the initial foaming. The 3D internal structure images of these specimens were acquired by using XRM available at the Argonne National Laboratory (ANL). These images were analyzed and the moisture dissipation processes in different types of asphalt binders were directly quantified. It was observed that the rate of moisture dissipation in high performance grade (PG) (stiff) binders was slower than that of low PG grade (soft) binders. It was also observed that the size distribution of moisture bubbles in the binders varied in different binders.

The present study investigates the use of heavy oil fly ash (HOFA) generated in the power plants as a stabilizer or fill material for various construction activities. To recycle the HOFA as fill material, it was mixed with Portland cement at different ratios. Laboratory batch and column experiments were performed on the HOFA and fill materials to investigate the leaching behavior and possible environmental impacts of the potentially hazardous elements such as arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), mercury (Hg), nickel (Ni), lead (Pb), copper (Cu), zinc (Zn), selenium (Se), and vanadium (V) within the HOFA. The results showed that leaching of toxic elements from the HOFA can pose toxicity to the environment, Whereas stabilized material prepared by HOFA mixed with 40% cement proved environmentally safe for construction uses.

This study investigates the effect of retention time of rice husk ash (RHA) combustion on its characteristics. The retention time was changed from 15 min up to 32 h. The chemo-physical and microstructural properties characterization methods included monitoring of electrical conductivity and pH variations of saturated lime–RHA solution, X-ray fluorescence, and diffraction. To assess the pozzolanic performance of RHA, a control mortar was produced as a reference with a water-to-cement ratio of 0.45 and a flow of 84%, and three cement replacement percentages by RHA of 5, 10, and 15% were applied for each retention time. The results show that with an increase in retention time, the EC and pH changes steadily decrease, suggesting lower RHA reactivity at longer retention times. However, no crystalline phases were found in RHA up to 32-h combustion, primarily because of the rapid cooling of the yield ash. In contrast, the compressive strength of RHA blended mortars increases up to 4 h combustion and then decreases. A possible explanation for the lower strength activity of short retention time RHA is offered in this study.

Chloride-induced rebar corrosion is one primary cause of early cracking of reinforced concrete (RC). A model to accurately predict the time before steel corrosion and concrete cracking, with due consideration of the heterogeneous nature of concrete matrix, is highly desired by maintenance engineers. This paper presents the results of a research study directed at developing a stochastic numerical method to model the microstructure of concrete matrix and to predict the service life of RC in three key steps: chemical ingress, steel corrosion, and concrete cracking. The finite-element method (FEM) is employed to model the ingress of multiple chemical species into variably saturated concrete matrix. By using Faraday’s law, rebar corrosion is modeled in a mixed localized—uniform pattern and quantified as a transient displacement boundary condition for subsequent analysis of concrete cracking. The proposed FEM model is validated by using laboratory experiments and applied to predicting the corrosion-induced cracking of an RC bridge deck.

Lime generally improves the performance of soils. However, some cases reported an adverse effect. To develop an understanding of the underlying mechanisms, a systematic study covering a wide range of plasticity and mineralogy of soils was carried out. Six different soil samples were reconstituted using two extreme types of soils, in other words, a montmorillonite rich expansive soil and a silica-rich non-expansive soil. The influence of lime stabilization on these soils was evaluated through determination of geotechnical properties such as liquid limit, plastic limit, swell, compressive strength, mineralogy, and microstructure. An optimum lime content beyond which the strength improvement decreased was found. This phenomenon is more prominently observed with silica-rich soils that form silica gel. As the silica gel is highly porous, when formed in large scale the strength gain from cementation is substantially countered by the strength loss from gel pores, giving rise to a visible reduction in overall strength. Additionally, the gel materials hold a large amount of water, leading to increased plasticity and swelling. Therefore, excessive lime treatment should be avoided for silica-rich soils.

In recent years, the use of rubber from scrap tires to modify the mechanical properties of bituminous mixes has become increasingly important in road engineering. There is currently much research devoted to the influence of this waste material on mix performance. This paper presents a study of the incorporation of crumb rubber (by the dry process and the wet process) and its effect on the bearing capacity and cohesion of bituminous mixes. The results obtained show that crumb rubber increased the stiffness and stability of mixes although it slightly reduced their indirect tensile strength. Apart from the evident environmental benefits, adding this waste to asphalt mixes improves the long-term performance of road surfaces because it reduces the effect of traffic loads on the pavement.

Surveys on innovative materials for aircraft arrestor beds are of great interest in airport safety research. In the event of a runway overrun, the arrestor bed has to provide for the complete stop of the aircraft. In doing so, the bed essentially collapses under the effect of the vertical load of the nose and main gears. Along the contact areas between the wheels and bed, the horizontal drag forces generated depend on the dissipative properties of the material used in the bed. The use of innovative materials in arrestor beds could lead to a significant improvement in the performance of same. In the paper, the authors propose a cellular mortar with expanded polystyrene spheres and the use of static and dynamic tests to determine its characterization. The aim is to optimize its composition in terms of mechanical properties, to evaluate its durability under the effects of environmental actions, and to estimate the stopping distances for selected aircrafts. The code arrestor provided by the Federal Aviation Administration (FAA) was used as a reference for distance calculations.

For several years, 18-mm- (0.7 in.-) diameter strands have been successfully used in cable bridges and for mining applications. The use of these large diameter strands in pretensioned concrete girders could allow approximately 35% increase in the prestressing force compared to the same number of 15-mm- (0.6 in.-) diameter strands and 92% increase compared to 13-mm- (0.5 in.-) diameter strands. Consequently, this process will allow for longer spans, shallower structural depth, and/or wider girder spacing in bridge construction. For the same prestressing force, the use of 18-mm- (0.7 in.-) diameter strands results in fewer strands to jack and release, fewer chucks, and greater flexural capacity due to lowering the center of gravity of the strands. Despite the advantages of using large diameter strands in pretensioned concrete girders, the lack of data on their mechanical and bond properties hinder their wide use in bridge construction. In this paper, the mechanical and bond properties of 18-mm- (0.7 in.-) diameter strands are evaluated. One hundred and two strand specimens were obtained from different strand producers and production cycles to evaluate the ultimate strength, yield strength, modulus of elasticity, and elongation at two different laboratories. Test results indicated that all strands adequately met the requirements of the ASTM standard A416-06, with the exception of the minimum yield strength requirements (90% of the specified ultimate strength). The power formula for stress-strain relationship was used to provide an accurate predictor of the behavior of strands. Also, 58 strand specimens were tested for their bond in mortar and concrete using the North America Strand Producers (NASP) test method. Test results demonstrated that the bond of 18-mm- (0.7 in.-) diameter strands is proportional to the concrete strength. A formula for predicting the NASP pull-out test value as a function of concrete strength was also developed. In addition, NASP test results for clean and rusted strands were measured and compared at different slip values.

Utilization of fly ash in concrete reduces the use of virgin materials and offers benefits of reduced landfill materials and ${\mathrm{CO}}_2$ emissions avoidance—fly ash therefore contributes to industrial sustainability. This paper presents a method to optimize the cement and fly ash contents in concrete on the basis of the hardened concrete properties testing and environmental effects. Such fly ash concrete would develop an adequate 1-day and 28-day compressive strength and would be as durable as the ordinary portland cement concrete. Nine concrete mixtures with fly ash contents ranging from 15–60% and cementitious material contents from $338–391\mathrm{kg}/{\mathrm{m}}^3$ ($570-705\mathrm{lbs}/\mathrm{cu}\mathrm{yd}$) were investigated. Environmental life cycle assessments (LCA) were completed by using a model developed for Denver, Colorado. The optimized fly ash concrete was selected to yield a similar 28-day compressive strength and durability to that of Colorado Department of Transportation (CDOT) Class D structural concrete. The durability aspects investigated included the resistance to rapid chloride-ion penetration and the resistance to the rapid cycles of freezing and thawing. The results show that the mixtures with cementitious material content lower than $365\mathrm{kg}/{\mathrm{m}}^3$ ($615\mathrm{lbs}/\mathrm{cu}\mathrm{yd}$) and fly ash content higher than 40% meet the CDOT Class D structural concrete strength and durability requirements. On the basis of the structural performances of the concrete mixtures and environmental effects, the optimized cementitious material content and the maximum possible cement replacement percentage with the fly ash was selected to be $338\mathrm{kg}/{\mathrm{m}}^3$ ($570\mathrm{lbs}/\mathrm{cu}\mathrm{yd}$) and 50%, respectively. The optimized concrete mixture exhibited excellent characteristics in compressive strength (32.0 MPa, 4,635 psi at 28 days), resistance to chloride-ion penetration (moderate at 28 days of age) and freeze-thaw (96, average durability factor after 300 cycles). The mixture with optimum fly ash and cementitious content had the minimum embodied energy and greenhouse gas (GHG) emission among the nine mixtures. The embodied energy and GHG emission of the optimized concrete mixture (per cubic meter) were 2,643 MJ and $361\mathrm{kg}{\mathrm{CO}}_2\mathrm{E}$, respectively, which are 32.8 and 35.2% less than the mixture with the most embodied energy and GHG emission.

The suitability of crushed concrete or recycled concrete aggregate (RCA) materials has been evaluated for use as pavement material for unbound basecourses. This paper covers the general engineering properties and response to cyclic loading as determined by repeated load triaxial testing (RLTT). In Australia, pavements commonly consist of granular basecourses and subbases supporting thin bituminous seals (asphalt or spray—chip seal). In this paper, a study is presented of the performances of three South Australian basecourse products, nominally 20 mm. The basecourse products included two RCA materials and a local virgin aggregate (quartzite). The resilient modulus and permanent deformation behaviour of RCA mixtures were investigated at different levels of moisture contents (90, 80, and 60% of optimum moisture content), subjected to a simplified stress regime suited to Australian construction. In terms of both resilient modulus and accumulation of permanent deformation, the RCA material performed better than the quartzite aggregate.

When steel-framed structures are exposed to fire, connections play a crucial role in transferring forces from highly stressed members to less stressed members. The performance of bolted connections, under ambient and fire conditions, depends on the strength characteristics of bolts. At present, the fire resistance of bolts is evaluated by assuming the high-temperature properties to be same as those of conventional mild steel. This is due to lack of data on high-temperature properties specific to high-strength steel bolts. To overcome this drawback, high-temperature thermal and mechanical properties of Grade A325 and A490 high-strength steel bolts are evaluated. Thermal conductivity and specific heat of A325 and A490 were measured in the temperature range 20–735°C, whereas thermal expansion was measured in the range 20–1000°C in both the heating and cooling phases of fire. Steady-state single shear and tension tests were carried out on A325 and A490 bolts at 20–800°C. Results from these tests were used to generate thermal conductivity, specific heat, thermal expansion, shear, and tensile strength relationships as a function of temperature for A325 and A490 bolts. Test data indicate that strength properties of A325 and A490 steel degrade faster than those of conventional steel and also that A490 steel exhibits slightly higher strength and stiffness properties than A325 steel at 20–800°C.

It is a well-known fact that waste products are available in large quantities within industries where they are generated. Therefore, this study investigates the incorporation of the agricultural and industrial residue of rice husk ash into the cement-stabilized rammed earth system to recover the use of raw land as a sustainable construction material and provide low pozzolanicity content rice husk ash with a suitable end purpose. The best-suited mixture to meet the normal masonry requirements was selected for the construction of a prototype building, which underwent technical assessment of its structural and thermal performance and of the durability of its cement-stabilized rammed earth-rice husk ash walls. The results showed that sandy soil, when partially replaced by the maximum ash content of 7.5% and stabilized with 10% cement, proved to be a promising alternative material. It proved to be a high-quality construction material that can be used to build energy-efficient houses and considered in the issue of social and environmental sustainability.

The diffusion of chloride ions is one of the main factors that arouses steel corrosion in concrete. In this paper, a two-dimension cellular automaton (CA) model was developed to simulate the diffusion process of chloride ions in concrete. The evolution rules of the proposed CA model were validated by comparing with the Fick’s second laws (FSL), and the distinctions between the CA model and the FSL were discussed pertaining to calculation methods and substantive characteristics of chloride ion penetration in concrete. Further, an improved CA model is proposed, called the JPCA model, which considers the jump probabilities of chloride ions varying with diffusion times and depths. The numerical simulations demonstrate that the computation results on the basis of the JPCA model are closer to the experimental data than those derived from the FSL. The JPCA model proposed in this paper provides a new way to study concrete suffering from chloride ion penetration.