Journal of Materials in Civil Engineering

Architectural and decorative concrete (ADC) has become an enormously popular product for both building interiors and exteriors, combining an aesthetic finish with structural capabilities. Cracking and chipping of ADC product during handling and transportation, however, is of great concern due to the brittleness of ADC materials. This paper looks at the development of a white strain-hardening cementitious composite (SHCC) as an alternative ADC material to address the above-mentioned challenges. It was found that the replacement of ordinary portland cement and fly ash with white cement altered SHCC microstructure which is unfavorab to the tensile strain-hardening behavior. A micromechanical model was engaged for composite optimization through ingredients selection and component tailoring to reengineer white SHCCs.

This paper considers the effect of the thermophysical properties of concrete on temperature distributions and stresses developed in concrete pavements. The temperature distributions in concrete pavements, composed of different thermophysical properties, were calculated using a finite-difference model. These temperatures were then fed into a finite-element model as thermal loads in order to calculate tensile stresses in the concrete. It was found that the thermophysical properties of concrete can significantly influence the magnitude of tensile stresses and, subsequently, the thickness of the concrete slab. Concrete with higher thermal conductivity and diffusivity (e.g., incorporating high conductive aggregates and/or metallic fibers) will experience much more uniform temperature and, as a result, a smaller tensile stress will be developed in the concrete. Increasing the thermal conductivity of concrete from $1.2\mathrm{W}/\mathrm{m}\mathrm{K}$ (concrete containing limestone aggregates) to $3.6\mathrm{W}/\mathrm{m}\mathrm{K}$ (concrete containing quartzite aggregates and 1% metallic fibers) could result in a 25% reduction of the concrete slab thickness.

In this paper, various nanomechanical and macromechanical techniques were used to study the effect of a reclaimed asphalt pavement (RAP) binder on the microstructure and properties of a virgin asphalt binder and to evaluate the degree of blending that occurs between those binders. To this end, different atomic force microscopy (AFM) experiments (i.e., AFM tapping mode imaging, AFM nanoindentation, AFM force spectroscopy experiments) were conducted on a virgin asphalt binder, a recovered RAP binder, and their composite. In addition, dynamic shear rheometer (DSR) tests were conducted on the evaluated binders, and the dynamic modulus tests were performed on mixtures prepared using those binders to evaluate the degree of RAP blending and compare it with those obtained using the AFM test results. The results of the AFM images indicated that blending between the RAP and virgin binders occurs at the nano/microscale level in the composite binder at a fairly uniform manner. Furthermore, the nanoindentation test results indicated that the composite asphalt binder had a significantly lower modulus than the RAP binder and closer to the virgin binder; however, the virgin binder modulus was still significantly lower than that of the composite. The force spectroscopy results indicated that the RAP had adverse effects on the adhesion properties of the composite binder. The results of the DSR tests showed similar trends to that observed using the AFM nanoindentation results; however, the DSR was found to underestimate the effect of the RAP binder on the mechanical properties of the composite. Finally, the AFM test results suggested that about 85% of RAP was effective in the composite.

In this paper analytical formulations are developed for predicting the punching resistance of flat slabs of steel fiber–reinforced concrete (SFRC) flexurally reinforced with steel bars. By performing statistical analysis with a database that collects experimental results on the characterization of the postcracking behavior of SFRC, equations are determined for evaluating the residual flexural tensile strength parameters ($f_{Ri}$) from fundamental data that characterize steel fibers. The $f_{Ri}$ strength parameters proposed by CEB-FIP 2010 were used for the definition of the stress-crack width law ($\sigma \text{-}w$) that simulates the fiber-reinforcement mechanisms in cement-based materials. The second part of the paper describes an analytical formulation based on the concepts proposed by Muttoni and Ruiz, where the $\sigma \text{-}w$ law is conveniently integrated for simulation of the contribution of steel fibers for the punching resistance of SFRC slabs. By using a database composed of 154 punching tests with SFRC slabs, the good predictive performance of the developed proposal is demonstrated. The good performance of this model is also evidenced by comparing its predictions to those from other models.

In this study, quantitative analysis of the combined effects of fly ash and lithium admixture in mitigating alkali-silica reaction (ASR) in portland cement mortars prepared with Spratt limestone was investigated. The results from this investigation suggested that mortar bar expansions could be correlated with specific oxide(s) content in the fly ash through exponential relationships. The dosage of lithium nitrate required for ASR mitigation in mortars containing fly ashes having CaO content less than 23.50% was found to be less than that in the control mortars. Since lithium nitrate was found to be effective in reducing the expansions of control (no fly ash) mortars and mortars containing fly ashes, economic solutions can be obtained in both. However, the use of lithium nitrate was not needed for mortars containing fly ashes having CaO content less than 14.40%. A linear relationship between the oxide content of fly ash and the lithium dosage was found to exist, that can be used to optimize the lithium dosage as a function of fly ash composition to provide an economic solution for ASR mitigation.

As oriented strand board (OSB) increases in use, improving the mechanical properties is of importance. Improved in-plane shear properties will allow for more efficient use as well as open up other opportunities in engineered wood products with high shear stresses. Based on classical laminated plate theory, composite laminates with $\pm 45°$ laminate alignment patterns produce higher in-plane shear modulus and strength compared with typical $0°/90°/0°$ alignment. Oriented strand board was manufactured 13.3-mm thick with $0°/+45°/-45°/-45°/+45°/0°$ and $0°/90°/0°$ alignment patterns, and in-plane shear, bending, nail connection, and small-scale shear wall properties compared to commercial OSB. Results showed a 24% increase in shear modulus for the $0°/+45°/-45°/-45°/+45°/0°$ alignment when compared with the $0°/90°/0°$ alignment using a method similar to a standard in-plane shear test. Results also show 10% reduction in bending modulus of elasticity in the parallel direction. Small-scale shear wall tests were insensitive to changes of in-plane shear properties. Lateral nail connection tests showed no reduction in connection yield load, implying that these panels can be used in similar applications without affecting connection properties.

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 ($<100\mathrm{nm}$). 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 empirical estimation equations for pore-size distribution are developed for cement, mortar, and concrete, which can be used for refined modeling and simulating of durability-related issues, such as frost action, water permeability, and drying shrinkage.

Fatigue cracking, either top-down or bottom-up, is one of the major distresses in asphalt pavements. One of the significant challenges in predicting the fatigue cracking behavior of asphalt concrete is that such behavior, unlike that of elastic materials, depends on external conditions, such as temperature and loading rate within the nondamage or damage domain. The application of the viscoelastic continuum damage (VECD) approach or its further development, the viscoelastoplastic continuum damage (VEPCD) approach, requires extensive material testing of the viscoelastic properties (i.e., creep compliance or relaxation), uniaxial or multiscale fatigue tests, and computations, which may hinder the implementation of this fundamental approach for the characterization of fatigue for asphalt concrete. This study develops a new approach, based on a derivative of Poisson’s ratio, to characterize the integrity and material damage of asphalt concrete. Fatigue tests are conducted for two mixes at different load levels and temperatures. It is found that a unique relationship exists between the dynamic modulus and strain ratio. Mastercurves are constructed to determine the damage evolution in asphalt concrete during fatigue tests, which provides the basis for developing constitutive models to predict the fatigue life of asphalt pavement.

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 and WR. Field tests were undertaken with nuclear density gauges (NDG) and Clegg impact hammers (CH) to assess the performance of the various trial pavement sections. The recycled glass blend with 20% glass content was found to be the optimum level, where the blended material was workable and also had sufficiently high strength. The field testing results indicated that FRG blends are suitable in pavement subbase applications and is a viable additive when used in limited proportions with other recycled aggregates in pavement subbases. FRG blends may, however, not fully meet specified requirements as a pavement base material.

This research investigates the influence of aggregate gradation on the clogging characteristics of porous asphalt mixtures. Ten representative gradations used for open graded friction course (OGFC) applications from across the United States were used in this evaluation. The aggregate gradation was found to be strongly correlated to the macrotexture depth of the porous pavement and the permeability of the mixes both before and after clogging. Utilizing graded sand as the clogging material, it was also found that the operational (or secondary) clogging rate is approximately half of the measured initial clogging rate. Additionally, the operational clogging rate can be estimated from the $R_{15}$ value for the system, which is the ratio of the $D_{15}$ of the porous asphalt gradation to the $D_{15}$ of the clogging material.

Cores with diameters of 74 mm and length-to-diameter ($l/d$) ratios of 0.5, 1.0, 1.5, 2.0, 3.0, and 4.0, were removed from concrete beams. Compressive strength tests were conducted on 300 core specimens. The compressive strengths of concrete cores were fitted to the modified Weibull distribution. This information is useful in the theoretical description of concrete failure. Furthermore, on the basis of the Kolmogorov-Smirnov goodness-of-fit tests, the test data have been verified to follow this modified Weibull distribution. In addition, the modified Weibull model can predict the length effect more accurately than the conventional model.

Many basic igneous rocks contain smectite clays as a result of deuteric alteration during their formation or subsequent chemical decomposition. This has resulted in numerous failures when such materials are used in road construction due to inadequate durability. Various methods for assessing material durability have been developed and those using ethylene glycol (EG) to expand smectite clays appear to be the most effective. Protocols have been developed for a number of tests using EG, but it can be difficult to quantify the results in terms of unique values and develop specification limits for use in road construction. A simple new protocol for an EG soaking test, the modified ethylene glycol durability index (mEGDI), has been developed and the proposed interpretation of results is compared with existing specifications in this paper. The mEGDI is suitable for use as a screening test to identify poor-durability materials. However, inconsistent correlations with existing specifications exist for materials classified as durable by the mEGDI test and such materials require traditional testing before acceptance. The development of a rapid mEGDI is being investigated to reduce the time required to complete the test and therefore provide a useful screening test methodology.

Twelve commercially available tropical wood natural fiber species and their cementitious composites were thoroughly studied for possible production of natural fiber cementitious composites (NFCCs) through (1) the determination of chemical constituents of the fiber species, (2) determination of compatibility of natural fiber cement and correlation of the compatibility with chemical constituents, and (3) examination of the mechanical property of NFCC and its correlation with the compatibility and chemical constituents of wood natural fibers. The results showed that (1) the chemical constituents of the 12 tropical wood fibrous materials varied considerably from one another, with cellulose content ranging between 40 and 57%, lignin ranging between 21 and 34%, and solubility ranging between 2.40 and 29.06% depending on the type of solutions, (2) pH values were below 7 for all natural fibers tested (pH of 3.36–6.22), and the acid-to-base ratio (ABR) values were no greater than 1, indicating that the base buffering capacity (BBC) values were higher than the acid buffering capacity (ABC) values, (3) the compatibility reduced as the wood natural fiber content increased and was polynomially correlated to the solubility of the wood natural fiber species, (4) mechanical properties of NFCC decreased as the fiber content increased, with the highest bending strength (7.21 MPa) and compressive strength (33.18 MPa) for movingui NFCC corresponding to the lowest hot water and $\mathrm{Ca}(\mathrm{OH}{)}_2$ solubility; the lowest bending and compressive strengths (0 MPa) were for both moabi and doussie NFCCs corresponding to their high solubility contents, and (5) the five best natural fiber species studied for NFCCs were movingui, nkanang, eyong, tali, and padauk, whereas the least suitable two were moabi and doussie. The results provided a fundamental and essential database and technologies for better understanding tropical wood natural fiber species to use them as value-added commercial products in the construction industry and further academic research.

The building sector is widely recognized as having a major impact on sustainable development. Both in developed and developing countries, sustainability in buildings approaches are growing. Laterite dimension stone (LDS) is a building material that was traditionally used in sub-Saharan Africa, but its technical features still need to be assessed. This article presents some results of a study focused on the characterization of LDS exploited in Burkina Faso for building purposes. The measured average thermal conductivity is $0.51\mathrm{W}/\mathrm{mK}$, which increases with water content and evolves with the specific gravity and with porosity. Rock mineral phases (quartz, goethite, hematite, magnetite) are cemented by kaolinite. The porosity of the material is high (30%), with macropores visible on the surface and found in the rock inner structure as well. Results from the hygrothermal monitoring of a pilot building are also presented.

Lightweight air-trapped cemented soils are prepared by mixing air bubbles and water with sand and cement. Inappropriate curing temperatures can negatively affect the properties of lightweight air-trapped soil (ATS); however, the effect of the curing temperature has not been studied. This experimental study was conducted to investigate the effect of curing temperature on the properties of lightweight ATS. Three different unit weights of lightweight ATS, 6, 8, and $10\mathrm{kN}/{\mathrm{m}}^3$, and temperatures ranging from $-5$ to 40°C were considered. Based on the results of unconfined compressive strength tests, an allowable curing temperature range of 5–25°C is suggested to ensure a suitable compressive strength of lightweight ATS. Based on measurements of volume change, an allowable range of temperature that results in volume change within the permissible range is 8–25°C.

The development of cross-laminated timber (CLT) technology has opened up new opportunities for low-density hardwood species, which have traditionally not been rated as construction-grade materials for structural engineering applications. Several characteristics of CLT, namely thermal performance, seismic behavior, and speed of construction, have raised interest among designers. The CLT technology has recently been used for residential and nonresidential multistory buildings and it has been identified as one of the ways of achieving tall timber building construction. As CLT gains acceptance in the industry, low-density wood species, not specified in current ANSI standards, need to be investigated for potentially successful use in CLT panels. This paper presents a study that demonstrates the viability of a Forest Stewardship Council (FSC) certified sustainable plantation grown low-density species, hybrid poplar (marketed as Pacific Albus), for use in performance-rated CLT panels by following the ANSI/APA PRG-320-2012: Standard for performance-rated cross-laminated timber shear and bending test guidelines to determine the structural viability of the CLT panels.

The incorporation of carbon nanofilaments in cementitious materials has been researched extensively in the past decade. However, the poor dispersibility of these filaments remains a hurdle to harnessing their exceptional properties. This work presents a method for enhancing the dispersion of carbon nanofibers (CNFs) in cementitious matrices. The method incorporates silica fume to stabilize the distribution of CNFs in fresh cement paste. The investigations show that this method is significantly more effective than similar approaches. To examine the effectiveness of the method, specimens of CNF incorporated cement paste with different concentrations of silica fume were produced and imaged by optical microscopy. Using a novel dispersion quantification method, the dispersion values of CNFs in the specimens were measured and compared. The results show that silica fume, if used in sufficient proportions, can largely prevent the reagglomeration of CNFs in fresh cement paste, and thereby stabilize their dispersion.

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 recycled aggregate concrete can help to enhance the concrete’s performance and offset this higher susceptibility.

In the present study, cyclic behavior and liquefaction potential of pond ashes collected from Talcher, Panki, and Panipat ash embankments located in seismic zone III and IV have been studied. Cyclic triaxial tests were conducted on reconstituted pond ash samples at a relative compaction varying from 94 to 99%. The effects of loading frequency, confining pressure, and relative compaction on cyclic behavior and liquefaction potential of reconstituted pond ashes have been studied. From test results, it is seen that all compacted pond ash samples exhibit good liquefaction resistance, dynamic properties, and degradation index. It may be concluded that pond ashes from Talcher, Panki, and Panipat can effectively be used as a geomaterial in geotechnical applications.

The effectiveness of chopped carbon fibers to enhance the thermal conductivity of bentonite-based grout was examined. Fibers of 3 mm and 150 μm in length were added to sodium bentonite and silica sand mixtures at different volumetric concentrations. The thermal conductivity of the resulting composite material was then measured using a non-steady-state needle probe technique. The conductivities of the fibrous materials were compared to bentonite and sand mixtures containing natural flake graphite and milled, compressed exfoliated graphite at corresponding volumetric concentrations. The resulting conductivities for all tested materials increased with the volumetric fraction of additive. However, the 3-mm carbon fibers were more effective as compared to either granular graphite; at a volume fraction of 0.68% the 3-mm fibers were approximately twice as effective as either form of graphite.