Journal of Materials in Civil Engineering

This paper describes the results of an experimental study that was performed to obtain desorption isotherms for a wide range of fine lightweight aggregates that are used commercially in North America. The desorption isotherms were determined for the entire gradation of the fine lightweight aggregates (as received). To obtain the desorption isotherms a pressure plate apparatus (porous plate) was used. The pressure plate enables the desorption isotherm to be measured at high relative humidities (beginning at 100%). In addition to providing experimental results obtained with the pressure plate method, desorption results obtained by gravimetric desorption and dynamic vapor desorption methods are also provided. The gravimetric desorption and dynamic vapor desorption methods are generally used at lower relative humidities (98% and 0% relative humidity). The results indicate that water leaves the fine lightweight aggregates at relative humidities as high as 99.9%. This suggests that internal curing water is available to the cement matrix even at relatively high water-to-cement ratio mixtures when the suction forces exerted by cement paste are small. The results of this work are helpful for the development of mixture proportioning techniques and numerical simulation for internally cured concrete mixtures.

This research examines the efficiency of thermomechanical pulp (TMP) fibers, both untreated and after chemical treatment to produce holocellulose and $\alpha$-cellulose, for internal curing. In addition, the effect of TMP fibers on early hydration behavior was investigated. The results show that TMP and $\alpha$-cellulose fibers had a negligible effect on cement hydration. Holocellulose, conversely, significantly reduced the rate of hydration, noticeably delaying setting time. The addition of the fibers in dosages to provide an additional amount of entrained water of 0.05 g per gram of cement resulted in a decrease of early autogenous shrinkage of cement paste. Holocellulose, reducing autogenous shrinkage of cement paste by 93%, was shown to be the most effective for internal curing; however, its adverse effect on cement hydration may require acceleratory admixtures when used in concrete. Thermomechanical pulp and $\alpha$-cellulose showed a similar efficiency in mitigating autogenous shrinkage; these fibers reduced shrinkage of cement paste by approximately 51 and 45%, respectively.

Although superabsorbent polymers, especially polyacrylamides, have been successfully used as internal curing agents in concrete for over a decade, the absorption and desorption behaviors, which are key factors in determining the effectiveness of internal curing, are not yet fully understood. Polyacrylamides tend to deprotonate in a high pH environment, allowing superabsorbency of high pH solutions, but their structure is very sensitive to changes in ionic content and concentration of the surrounding solution. This work is aimed at demonstrating how polyacrylamides with very similar chemical compositions can behave differently as they are exposed to different solutions. In parallel, two solutions with the same pH can cause the same polyacrylamide to swell differently. Spontaneous swelling and deswelling behavior in saturated conditions is observed under significant changes in the ion concentration of the surrounding solution. The polyacrylamides used in this work also show strong ion filtration behavior, as observed through analyses of the surrounding pores' solution.

Natural pozzolans (NP) have proven to be an effective supplementary cementitious material; however, the replacement of ordinary portland cement (OPC) with NP might increase the autogenous and drying shrinkage of concrete. Internal curing (IC) might be of great help when using NP because it can promote the pozzolanic reactions and reduce shrinkage. The aim of this research is to assess the effect of IC in concrete containing NP. Results indicate that a 39% replacement of OPC with NP decreased compressive strength by 15%, decreased chloride ion permeability by 66%, and increased autogenous shrinkage by 40%. IC with prewetted lightweight aggregate showed no significant effect in compressive strength or permeability, but it decreased autogenous shrinkage by up to 58%. NP used in this investigation presented higher chemical shrinkage than OPC, making IC less effective as levels of NP increased. The important decrease in permeability attained through the use of NP and the higher chemical shrinkage of NP makes IC a critical technology to consider in concrete mixtures with NP.

In the past 10 years, renewed research interest has shown the benefits of internal curing by incorporating prewetted lightweight fine aggregate (LWFA) in high-performance concrete (HPC). To determine the optimum LWFA content, information about the propensity for shrinkage in the cement paste, specifically the chemical shrinkage value, is needed. However, information is lacking on how to determine the long-term chemical shrinkage value for HPC with supplementary cementitious materials (SCMs) and/or shrinkage-reducing admixture (SRA). The purpose of this research was to identify a simple procedure to determine long-term chemical shrinkage values for given cementitious systems with SCMs and/or SRA. Several improvement to ASTM C1608 (dilatometry procedure) were investigated. An experimental prediction model was adopted and verified to estimate long-term chemical shrinkage values for portland cement systems containing SCMs and/or SRA. A recommended procedure is proposed to determine the long-term chemical shrinkage values for HPC systems containing SCMs and/or SRA, and a modification to a commonly used LWFA proportioning equation is suggested.

Fine lightweight aggregate (LWA) is being increasingly used for the manufacture of internally cured concrete. Internally cured concrete can be viewed as a concrete that contains fluid (water) in the pores of the LWA (or other porous inclusions) that can be released to the paste after setting. Most research performed on internally cured concrete assumes the LWA has been prewetted for some time before mixing (generally lab studies use 24-h soaking, whereas this value varies in practice). The research described in this paper investigated the potential for using aggregate that begins the mixing process from a different moisture state (i.e., not 24-h prewetting). Specifically, this paper considers oven-dry aggregate as a worst-case scenario to determine how much water would be absorbed by the LWA during the mixing and placement processes. To determine the amount of water absorbed by the LWA, isothermal calorimetry was used. Two different mixing scenarios were investigated, showing that 56–71% of the 24-h water absorption could be achieved using the worst-case scenario of oven-dry aggregates. Although the use of oven-dry aggregate would be extremely rare for a field application (except for possible application to bagged products), this approach could be extended to include fine LWA with other initial moisture conditions.

The mobility of water in hardening cement paste is an important aspect in view of the effectiveness of internal curing. A mechanistic-type numerical model of cementitious materials is applied for the analysis of water migration kinetics from internal curing agents [superabsorbent polymers (SAP)] into hydrating cement pastes with a low water-to-cement ratio. It is shown that the release of curing water at early age (i.e., during approximately the first day of hydration) allows for a uniform and practically instantaneous distribution of water within the whole volume of cured paste, even if the distances for water migration are as high as 2–3 mm. The evolution of permeability as a result of the hydration process is shown to have a major impact on the mobility of water in the cement paste. The depercolation of capillary porosity may substantially inhibit the water transport. The analysis shows that a part of the water first received by the paste in the proximity of the SAP can be later redistributed to a large volume of hardening paste, even after the permeability has become very low.

Three viscosity modifiers (a commercial shrinkage-reducing admixture, a polypropylene glycol, and a cellulose ether) are used to reduce the effective diffusivity of chloride ions through mortars during a 1-year exposure. Two delivery mechanisms were studied: (1) adding a viscosity modifier to the mix water and (2) diluting the viscosity modifier in water, prewetting fine lightweight aggregate (LWA) with the solution, and replacing a portion of the sand with the prewetted LWA, which is equivalent to the practice of using LWA for internal curing. After a 28-day curing period, the cylinders were submerged in a 1-$\mathrm{mol}/\mathrm{L}$ chloride solution. After 24 and 52 weeks of exposure, micro X-ray fluorescence analysis was used to profile the radial chloride concentration under ambient air pressure. The effective diffusivity was estimated by regression, assuming ideal Fickian radial diffusion. Compared with the control mortar (no admixture, no LWA), the addition of the viscosity modifier to the mix water reduced the effective diffusivity by nearly a factor of two, and using LWA saturated with a viscosity modifier reduced the effective diffusivity by a factor greater than two. Therefore, the use of these viscosity modifiers has the potential to double the service life of any concrete that may be subjected to degradation that depends on diffusion, such as corrosion of the steel reinforcement and sulfate attack.

Early-age cracking in bridge decks is a severe problem that may reduce functional life of the structure. The effect of lightweight fine aggregate on the cracking tendency of bridge deck concrete was evaluated using cracking-frame testing techniques. Water for internal curing is provided by incorporating prewetted absorptive lightweight aggregate (LWA) into the mixture during batching. The absorbed water within the LWA is desorbed at early ages as hydration progresses. The release of the internal curing water increases cementing material hydration and reduces capillary stress caused by self-desiccation. Cracking frames measure the development of stresses due to thermal and autogenous shrinkage effects from setting until the onset of cracking. Restrained concrete specimens were tested under temperature conditions that match those of an in-place bridge deck and under isothermal curing conditions to determine the stress development due to autogenous shrinkage. Internal curing from LWA increased the time to initial cracking, reduced autogenous shrinkage stress development, and increased the degree of hydration in bridge deck concretes.

During a freezing event, pore solution in cementitious bodies expands and creates stresses that can cause damage; therefore, reducing the number of freeze/thaw cycles experienced by a structure will extend the structure’s service life. The incorporation of phase-change materials (PCMs) to reduce the number of freeze/thaw cycles experienced by bridge decks has been investigated by modeling, mechanical testing, calorimetry, and X-ray microtomography. Models identified geographical regions in which freeze/thaw damage is not a significant concern and regions where this technology may be practical, increasing the service life of a bridge deck by at least 1 year. The incorporation of PCM reduces strength by varying amounts and for varying reasons, depending on which PCM is used and how it is introduced into the concrete. Because a variety of methods exist to address this loss in strength, PCM incorporation shows promise as a technique for addressing one aspect of worldwide infrastructure maintenance challenges.

This paper compares the effect of type of compaction (impact and gyratory compaction) on mechanical properties (such as water sensitivity and stiffness modulus) in warm-mix asphalts. Moreover, the manufacture and laying temperatures and the use of additives for warm-mix asphalts have been taken into account. The mixes tested have a semidense aggregate gradation with a B-60/70 penetration binder and different types of warm-mix additives have been added. The mixtures compacted by gyratory compactor at different temperatures all displayed good behavior in terms of water sensitivity; in contrast, not all mixtures compacted by impact achieved this. On reducing the manufacturing temperature, the stiffness moduli decreased in all mixtures for both types of compaction, this reduction being less pronounced in the mixes manufactured with the gyratory compactor. The results have been evaluated statistically.

Ultra high performance concrete (UHPC) is well suited to provide adhesive connections with other materials. Here, not only does mechanical interlocking provide adhesion, but also intermolecular forces that are closely related to the surface energy of the used materials. The determination of intermolecular forces for UHPC connected to glass and steel is presented in this work. First, the theoretical relation between intermolecular forces and the surface energy is shown. The main part deals with experiments on the determination of the surface energies. Contact angle measurements are used to determine surface energies of steel, glass, and hardened UHPC. Some ideas on estimation of the surface energy of fresh UHPC using conventional testing methods are presented. Finally, the calculated specific adhesion is compared to the technical adhesion determined by direct tension tests.

Effectiveness of cement kiln dust (CKD) in improving the stiffness of recycled base course materials was studied using both seismic modulus and bench-scale resilient modulus tests. Recycled materials included road surface gravel (RSG) and recycled pavement material (RPM). The modulus of RPM and RSG specimens mixed with CKD increased 5–30 times compared with untreated materials; however, the improvement was not as high as cement stabilization. Modulus generally increased with curing time with more hydration; however, decrease in the modulus of the RPM mixed with 15% CKD during curing is attributed to swelling potential of the CKD. Lower rate of increase in modulus of CKD mixtures compared with cement mixtures with curing time was attributable to the chemical composition of CKD, i.e., high free lime and sulfate contents. Freeze-thaw durability tests resulted in modulus reduction on the order of 0.5 to 0.8 for CKD mixtures and 0.5 for cement mixtures. Attributable to the combined effects of stiffness gain with continuing hydration and stiffness reduction with freeze-thaw cycles, the final modulus of the recycled materials mixed with CKD is 2 to 5 times higher than that of untreated RPM and RSG materials. This study also showed that modulus change of stabilized granular materials can be estimated from seismic Young’s modulus.

Lime stabilization prevails to be the most widely adopted in situ stabilization method for controlling the swell-shrink potentials of expansive soils despite construction difficulties and its ineffectiveness in certain conditions. In addition to the in situ stabilization methods presently practiced, it is theoretically possible to facilitate in situ precipitation of lime in soil by successive permeation of calcium chloride (${\mathrm{CaCl}}_2$) and sodium hydroxide (NaOH) solutions into the expansive soil. In this laboratory investigation, an attempt is made to study the precipitation of lime in soil by successive mixing of ${\mathrm{CaCl}}_2$ and NaOH solutions with the expansive soil in two different sequences. Experimental results indicated that in situ precipitation of lime in soil by sequential mixing of ${\mathrm{CaCl}}_2$ and NaOH solutions with expansive soil developed strong lime-modification and soil-lime pozzolanic reactions. The lime-modification reactions together with the poorly developed cementation products controlled the swelling potential, reduced the plasticity index, and increased the unconfined compressive strength of the expansive clay cured for 24 h. Comparatively, both lime-modification reactions and well-developed crystalline cementation products (formed by lime-soil pozzolanic reactions) contributed to the marked increase in the unconfined compressive strength of the expansive soil that was cured for 7–21 days. Results also show that the sequential mixing of expansive soil with ${\mathrm{CaCl}}_2$ solution followed by NaOH solution is more effective than mixing expansive soil with NaOH solution followed by ${\mathrm{CaCl}}_2$ solution.

For designing pavements many state agencies, including those in Oklahoma, use the 1993 AASHTO Guide for Design of Pavement Structures, which is empirical in nature. However, the Mechanistic-Empirical Pavement Design Guide (MEPDG) is believed to predict pavement distresses in a more mechanistic approach, on the basis of material properties, local traffic, and climate conditions. Among material properties in the MEPDG, the dynamic modulus ($E^{*}$) of the asphalt mix is one of the key parameters necessary to achieve the highest level of design reliability. The present study was conducted to estimate $E^{*}$ values of two commonly used hot mix asphalt (HMA) mixes (S3 and S4) in Oklahoma. Different design reliability levels, on the basis of rheological properties of three performance grade (PG) binders, were considered. These asphalt binders were collected from three different sources in Oklahoma. Furthermore, sensitivities of major pavement distresses, namely, rutting, fatigue cracking, thermal cracking, and roughness to the design reliability, and asphalt binder type and source were evaluated by using the MEPDG software (Version 1.100). It was observed that rotational viscometer (RV) test data overestimate the $E^{*}$ values in the case of stiff binders. Conversely, dynamic shear rheometer (DSR) test data predict significantly lower $E^{*}$ values of asphalt mixes with all PG binders. Among distress factors, the rutting in HMA layers’ was found to be highly sensitive to the design reliability and asphalt binder’s PG grade. The asphalt binder source was also found to be somewhat sensitive to rutting. Other distresses were not significantly influenced by the design reliability, asphalt binder PG grade, and source. The findings of this study are expected to provide transportation professionals with a better understanding of material input parameters that influence $E^{*}$ values of asphalt mixes and pavement distresses, and assist in implementing the MEPDG for local conditions.

The low temperature fracture properties of polyphosphoric acid (PPA) modified mixtures are evaluated and compared with those of polymer modified mixtures. The main objective is to determine whether PPA can partially or completely substitute traditional polymer modifiers, without adversely affecting the mixture’s resistance to thermal cracking. Laboratory compacted and field cored test samples from the Minnesota Road Research Project (MnROAD) were tested using traditional methods as well as newly developed fracture testing protocols: indirect tensile test (IDT), semicircular bending test (SCB), and disk-shaped compact tension test (DCT). The effects of temperature, air-void content, comma and long-term aging on low temperature fracture properties were analyzed; and field performance observations of the test cells from MnROAD were discussed. On the basis of the analysis, the fracture resistance of the PPA modified mixture is less than that of the SBS modified mixture. However, when PPA is used to substitute part of the SBS, a mixture with fracture resistance comparable to that of the mixture modified with SBS alone is produced.

The present study focuses on surface wave propagation in cementitious material with inhomogeneity. Thin, flakey inclusions were added in contents of up to 10% by volume and different sizes inside the matrix to realistically simulate cracking. The results are focused on the attenuation created by the inhomogeneity. As damage is added up in content, the level of attenuation strongly increases for the whole examined frequency band. However, the size and the population of the inclusions present an equally strong influence on the attenuation. The distortion of the frequency content is also evaluated by spectral density functions, showing that simple waveform analysis can enhance the characterization of damage in addition to the valuable assessment based on wave velocity.

This study aims to investigate and quantify the fraction of clogging in pervious concrete samples cored from parking lots. Image observation, analysis, and processing of representative cores retrieved from parking lots enabled qualitative relation of porosity with clogging. Porosity profiles obtained from processing of computed tomography (CT) scanned images were used to assess the nature and extent of clogging. Significantly lower porosity values were computed for old cores compared to newer ones. It was also observed that samples manifested clogged behavior because of high cement paste (mortar) content. Porosities of samples were calculated, for comparison using a gravimetric method and the clogged fraction in the cores was quantified by recalculating porosities of specimens scanned after vacuum cleaning. X-ray CT scanning proved a useful tool to study clogging, and the clogged fraction varied from 1.48% in sample PL 12-1 to 11.15% in sample QP 45-3.

Lime–fly ash reactions play a key role in improving the mechanical strength and tailoring the permeability characteristics of compacted fly ash. Activation of fly ash–lime pozzolanic reactions should accelerate the rate of strength development and possibly mobilize higher compressive strengths, facilitating improved engineering performance of fly ash amended materials. This paper makes an assessment of activation of lime–fly ash reactions by curing compacted fly ash–lime specimens at ambient (25°C) and at elevated temperature (80°C). The kinetics of fly ash–lime reactions are examined by monitoring the reacted lime as a function of curing period and temperature. The influence of variations in fly ash/lime content and dry density on the compressive strength developed by specimens at both temperatures is evaluated. The thermodynamic parameters for the fly ash–lime reactions have also been examined. Experimental results showed that curing at 80°C for 24 h accelerated fly ash–lime reactions such that it caused the steam cured (SC) specimens to develop 1.21–2.44 fold larger strengths than room-temperature cured (RTC) specimens cured at 25°C for 28 days. Analysis of thermodynamic parameters indicated that the fly ash–lime reactions are thermodynamically favored at fly ash contents of 50–70% and lime additions of 16–20%, and the reactions are endothermic in nature.

This paper examines the nonlinear stress-strain behavior of lightly stabilized granular base materials and presents a method to predict them based on modified and extended Ramberg-Osgood expression from unconfined compression (UC) testing. A typical granular material was lightly stabilized with 0.5–3.0% cement-flyash (CF) as well as with 1.5–3.0% slag-lime (SL) and tested in UC with internal deformation measurement setup. This study indicates that the proposed mathematical model can accurately predict the nonlinear stress-strain relationships of the lightly stabilized materials obtained from the experiments. The parameters involved with the proposed model were initial elastic modulus $E_0$, 0.2% proof stress ${\sigma }_{0.2}$, ultimate strain ${\epsilon }_u$, and the exponents for quantifying the nonlinearity of the curves $n$ and $m$. Values of all the parameters were determined from the experimental stress-strain responses and reliable regression relationships were developed between these parameters and unconfined compressive strength (UCS).