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This paper presents an experimental study, including evaluation and modification, on using dehydrated cement paste (DCP) as a new type of cement additive. After a series of processes, normal DCP (N-DCP) was produced as before and a modified form of DCP (M-DCP) was produced as well. The cementitious characteristics of the groups with different kinds and contents of DCPs were evaluated by following/using the required water of standard consistency, setting times, and compressive strength development. A new concept-evaluating the strength contribution of DCPs by using the theoretical strength contribution (TSC)-is proposed in this paper. The experimental results show that N-DCP can be used as a new type of cement additive to artificially adjust the consistency, setting times, and compressive strength of cement. When the content of N-DCP is approximately 9.47%, the value of TSC can reach 20% after approximately 1 day. In addition, the M-DCP that was produced in this study can be used to maintain high requirements of compressive strength in practice. Comparing that value of the N-DCP/cement system, when the content of M-DCP is approximately 3.5%, the value of TSC can reach almost 40% at both early and later stages.

Ultra-high-performance fiber-reinforced concrete (UHPFRC) is a novel cementitious material with enhanced strength in tension and compression, and significantly high energy absorption in the postcracking region. The application of UHPFRC for the earthquake strengthening of existing structures could considerably improve the performance of existing structures due to its superior properties. There are published studies where the direct tensile and the flexural behaviors of UHPFRC have been investigated and the superior tensile strength and post-crack energy absorption have been highlighted. However, there are not any published studies on the performance of UHPFRC under cyclic loading. In this paper, the results of an extensive experimental program on UHPFRC under direct tensile cyclic loading are presented and a constitutive model for the response of UHPFRC under cyclic loading is proposed. The accuracy of the proposed model is validated using experimental results from various loading histories and for different percentages of fibers, and the reliability of the proposed model is highlighted.

The reduction of cement content and incorporation of high volume of supplementary cementitious materials (SCMs) are key factors for the design of environmentally friendly concrete (Eco-Crete). The effectiveness of incorporating an SCM to enhance rheological and mechanical properties and durability of concrete depends on the type and content of SCM, as well as the degree of dispersion of the binder resulting from the use of high-range water reducer (HRWR). An experimental investigation was undertaken to evaluate the effect of binary and ternary cementitious materials on the packing density of the binder and compressive strength at 7 and 56 days of cement paste. The influence of the dispersion state of the binder on packing density was evaluated using the wet packing density approach to determine the optimum water demand (OWD) needed to achieve maximum wet density. The effectiveness of incorporating a high volume of SCM to enhance packing density is shown to increase with an increase of HRWR dosage, resulting from a greater degree of dispersion of the binder. The incorporation of sufficient dosage of HRWR led to lower OWD needed to achieve maximum density and higher packing density. The coupled effect of these changes results in higher compressive strength. Compared to the packing density of 0.58 for binder with 100% cement, the use of SCMs in a well-dispersed system is shown to secure packing density of 0.60 to 0.73. The ternary binders containing 40 or 50% slag and 5 or 10% silica fume, by volume of total binder, can ensure lower OWD, greater packing density, lower CO₂ emission, and higher compressive strength. Such binder systems can be adopted for use in sustainable cement-based materials. © 2016, American Concrete.

High-volume fly ash (HVFA) concrete, which typically has 50 to 60% fly ash as the total cementitious material content, is widely used to achieve sustainable development in the concrete industry. Strength development and carbonation are critical research topics for using HVFA concrete. This paper presents a numerical procedure to evaluate the strength development and carbonation depth of HVFA concrete. This numerical procedure consists of a hydration model and a carbonation reaction model. The hydration model analyzes the fly ash dilution effect and the pozzolanic reaction. The amount of carbonatable materials, such as calcium hydroxide (CH) and calcium silicate hydrate (CSH), are calculated using reaction degrees of cement and fly ash. The compressive strength development of cement-fly ash blends are evaluated from CSH contents. The calculation results from the hydration model, such as the amount of carbonatable materials and the porosity, are used as input parameters for the carbonation reaction model. By considering the effects of material properties and environmental conditions, the carbonation reaction model analyzes the diffusivity of carbon dioxide and the carbonation depth of HVFA concrete with different curing conditions, different fly ash contents, and different water-binder (w/b) ratios.

A testing program was conducted to determine whether concrete masonry prisms constructed with Type M mortar and grouts containing high volumes of supplemental cementitious materials (SCMs) could meet minimum masonry compressive strength requirements. Research focused on replacing portland cement (PC) with Class F fly ash and ground-granulated blast-furnace slag (GGBFS) in quantities larger than those currently allowed by technical standards. In addition, the research evaluated the development of the compressive strength of the prisms with time. Thus, specimens were tested at 14, 28, 42, 56, and 90 days. The control prism group contained grout with only PC. In the second prism group, the grout had Class F fly ash replacing PC at rates of 45, 55, and 65% while in the third prism group the grout had Class F fly ash and GGBFS combinations replacing PC at rates of 65, 75, and 85%. The compressive strength of all prisms exceeded the minimum compressive strength requirement of 10.34 MPa (1500 psi) at 28 days, although the 65% fly ash grout mixture itself did not meet the minimum grout compressive strength of 13.79 MPa (2000 psi) at 28 days. A lower estimate of the ultimate strength of grouted prisms constructed with grouts containing high volumes of SCM can be estimated by multiplying the strength measured at 14 days by 1.2 and 1.3 for prisms with binary and ternary grouts, respectively.

The injection of cementitious grout into deteriorated civil structures is a common application for strengthening or repair purposes. The nondestructive estimation of the repair effect, which is always desirable, is not an easy task because geometry, constituent materials' property mismatch, and temperature-dependent hydration rate often impose difficulties to the characterization. In many cases, after the grout injection and the elimination of voids, the pulse velocity decreases unexpectedly, complicating the task of repair evaluation. In this work, an experimental study of stress wave propagation in concrete impregnated with injection cement is presented. It is revealed that, despite the common impression, wave velocity should not be expected to rise after repair in any case because the properties of grout are initially lower than the surrounding concrete. This effect can be emphasized by the low hardening rate that is imposed to the grout material in the case of low environmental temperature. The transmitted frequencies are also decreased shortly after injection and, therefore, the decrease of wave parameters such as velocity or amplitude should not necessarily be taken as a sign of unsuccessful repair or even deterioration.

Efficient repair of concrete pavements typically requires a rapid-setting material to accelerate opening the road to traffic. While numerous high-early-strength cementitious repair materials are commercially available, many of them are vulnerable to premature deterioration. On the other hand, despite its improved long-term performance, concrete incorporating fly ash is rarely used as a repair material due to the delay in setting time, strength gain, and microstructural development at early ages. Nevertheless, these performance limitations can be mitigated by incorporation of nanoparticles (for example, nanosilica) in fly ash concrete. In this study, an effort was made to develop nano-modified fly ash concrete as a repair material for concrete pavements. The performance of the newly developed mixtures was compared to that of two commercial cementitious products. The results indicate that the nano-modified fly ash concrete has balanced performance in terms of hardening time, strength development, bonding with substrate concrete, and resistance to infiltration of fluids and salt-frost scaling.

Degradation due to cyclic freezing and thawing is a major durability problem in the concrete industry. Since the early 1930s, air entrainment by surfactant chemistry has been used to improve the resistance to freezing and thawing of concrete. Despite its effectiveness, air entrainment is one of the most resource-demanding aspects of concrete production from a quality control perspective, particularly in ready mixed concrete. The focus of this study is a new microsphere-based admixture that has been developed to provide freezing-and-thawing protection of cementitious materials under cyclic conditions. This new technology is significantly different from current conventional surfactant-based chemistries and, consequently, it addresses and eliminates the typical issues associated with the traditional method of air entrainment. The paper will explain the mode of action of the new microsphere-based admixture that provides freezing-and thawing protection of concrete.

Graphite nanoplatelets were used to control alkali-silica reactions in concrete by enhancing the barrier qualities of cementitious binders and providing local reinforcing effects against the damaging expansive phenomena. Nuclear magnetic resonance (NMR) spectroscopy was used to monitor the changes in chemical environment that reflect upon alkali-silica reactivity. Laboratory experiments were conducted to evaluate the effects of graphite nanoplatelets on alkali-silica reactions (ASRs). Reactive flint aggregates were used to induce ASR. The ²⁹Si MAS NMR spectroscopy technique was employed for evaluating the changes in chemical environment by monitoring different silicate tethrahedra (Qⁿ) as a basis to quantify the progress of ASR in concrete materials prepared with and without graphite nanoplatelets. Quantitative evaluations of different Qⁿ species present in anhydrous cement, calcium silicate hydrate (C-S-H), and ASR products indicated that introduction of graphite nanoplatelets lowered the degree of polymerization of silicate tetrahedral in C-S-H. The reduction in the breakdown of the networked structure of silicate tetrahedra under accelerated ASR indicates that graphite nanoplatelets reduce the extent of ASRs.

The study reports a sustainable solution to enhance concrete durability performance by using recycled glass powder as a supplementary cementitious material. Portland cement was replaced at different contents: 15, 30, 45, and 60% by weight. All concrete mixtures containing glass powder showed lower permeability compared to plain concrete. Particularly, 30% was identified as the optimum replacement for glass powder because the highest compressive strength was achieved. For this replacement, chloride diffusion and migration coefficient, water penetration depth, and sorptivity were found to be reduced by 87, 36, 65, and 61%, respectively. The improvements in those transport properties are attributed to the pozzolanic reaction of glass powder, which turned calcium hydroxide into calcium-silicate-hydrates. The microstructure of the formed cement paste and interfacial transition zone is refined and less porous, and therefore more resistant to ingress of harmful fluids and agents.

Long foam index test times and the inability to characterize different loss on ignition (LOI) in cementitious materials using the same solution concentrations prompted an examination of different test solution concentrations for various fly ash samples. A 15-minute duration forced the test into a number of cycles where air-entraining admixture (AEA) drops with sensitivity compatible to the fly ash allowed diffusion and reaction consistency throughout all the tests, allowing both low- and high-carbon fly ash to be characterized uniquely. The absolute foam index, defined as the amount of undiluted volume of AEA solution added to obtain a 15-minute endpoint (limits 12 to 18 minutes) signified by 15-second metastable foam, uniquely characterized 15 fly ash samples with LOI values that ranged from 0.17 to 23.3%. The absolute foam index strongly correlated to LOI values for fly ash samples greater than 5% LOI but variability was observed in samples less than 5% LOI.

The injection of cementitious grouts by vacuum techniques is increasingly used in repair and new construction of post- tensioning members. A research program was undertaken to assess the effect of thixotropy on water retention and behavior of grouts placed using such techniques. Tests were conducted using specimens sampled right after mixing as well as after being subjected to vacuum to extract part of the free mixing water. Test results have shown that the partial or complete extraction of free mixing water due to vacuuming decreases flowability (flow time and mini-slump cone) and increases thixotropy of grouts, mostly due to increased cohesiveness and internal friction within the solid particles. Good correlations were established between extracted water and variations in thixotropy, air entrainment, wick-induced bleeding, unit weight, setting time, and compressive strength. Mixtures exhibiting more than 35% normalized extracted water are not suitable for grouting by vacuum techniques due to increased cohesiveness that hinders proper penetrability. A set of regression models was proposed to simplify product development and predict grout properties either in the fresh or hardened states.

While there is an increasing interest in using photocatalytic cement-based materials, a lack of an appropriate standard procedure for testing the photocatalytic activity and efficiency of such materials makes comparisons among materials and data from different sources challenging. Current standard test methods are not appropriate for assessing photocatalytic nitrogen oxide conversion by cementitious materials because the standards do not consider surface properties of cementitious materials, nor are the test conditions appropriate for evaluation of cementitious materials. Therefore, the main objective is to propose a standard procedure for assessing the photocatalytic activity of cement mixtures with TiO₂ additives and to define a parameter-the photocatalytic efficiency factor (PEF)-that could be used to compare the photocatalytic activity of different TiO₂ cement mixtures, even for extended exposure conditions. The use of PEF is demonstrated, and values of PEF ranging from 8.40 to 51.55 µmol·h⁻¹·m⁻² (0.78 to 4.79 µmol·h⁻¹·ft⁻²) was observed for mixtures with TiO₂ up to 15% replacement.

Many studies attention are being devoted to use of nano-scale silica particles in cementitious materials by considering the success of using silica fume in concrete as an active pozzolan. The effect of various types of nanosilicas (NSs), both in powder and colloidal forms, with specific surface area (SSA) from 80 to 380 m²/g (0.016 to 0.078 ft²/lb) on the mechanical properties of cement paste and mortar were studied. Results showed a substantial reduction in the workability of mixtures by adding NS particles. The compressive strength of specimens was not affected by NS in powder and colloidal form, but was only sensitive to changing SSA. The use of NS enhanced the strength of cement paste compared to the control mixture, and the level of improvement increased for higher dosages of NS. However, by increasing the SSA more than 90 m²/g (0.018 ft²/lb), the compressive strength of specimens decreased. A low percent of various NSs did not affect compressive strength of mortar. However, adding a high dosage of NS particles created the same effect as using microsilicas.

In this study, biomass and co-fired fly ashes are examined for use as supplementary cementitious materials. These ash sources are not addressed in the current American standard for fly ash and natural pozzolan use in concrete (ASTM C618-12a). The influence of these ashes on early-age hydration kinetics, workability, setting time, strength, permeability, and sulfate resistance is investigated. The findings demonstrate that co-fired fly ash, when conforming to current ASTM C618 specifications, can impart similar properties to concrete as coal fly ash. Thus, the potential of an ash to be used as a supplementary cementitious material is related to the chemical and physical properties of the ash, and not necessarily to its source (that is, coal or co-firing). Current standards should consider permitting co-fired fly ash sources that meet existing ASTM C618 requirements and any additional requirements deemed necessary to ensure their satisfactory performance when used in concrete.

A study on the behavior of a steel fiber-reinforced cementitious mortar (SFRCM) in a triaxial compression condition and a comparison of results with those of a common high-performance concrete (HPC) is presented. SFRCM with a high compressive strength seems to be a promising material in civil engineering applications. A series of cylindrical specimens of two types of SFRCM with 1% and 2% volume fraction of steel fiber and one type of HPC were prepared and tested under various confining pressures: 0, 5, 10, 15, and 20 MPa (0.72, 1.45, 2.18, and 2.90 ksi). In general, raising the confinement level increases the peak axial stress and the corresponding strain, while on the other hand this causes the specimens to behave more ductile. According to the results, the addition of steel fiber has meaningfully helped increase energy absorption capacity of the specimens. Finally, empirical equations were derived to predict the peak axial stress and the corresponding strain of the tested materials as a function of confining pressure for tested materials.

Rice husk ash (RHA) is a promising alternative cementitious material for use in sustainable concrete. While the performance and durability of RHA concrete has been extensively investigated, there is scant information on the interactions between RHA and superplasticizers (SPs). This paper thus focuses on the combined effects of RHA and five different SPs. Rheological investigations showed that high SP dosages were necessary because of the RHA particles’ water absorption. This reduction in available water led to an increased solid concentration and shear-thickening behavior. Calorimetric measurements showed that cement hydration was delayed by the elevated SP dosages (and not directly by the RHA). Moreover, dilution of the cement reduced the reaction intensity at early age. Using RHA increased compressive strengths at 28 days by up to 20%. Finally, this study illustrated the importance of preliminary SP optimization to fulfill the requirements of specific concrete applications.

Using supplementary cementitious materials (SCMs) to decrease concrete diffusivity, which slow the ingress of chlorides into concrete that results in reinforcement corrosion, is one of the most economical ways to increase concrete service life. To show the effect of ternary SCM blends on concrete diffusivity, bulk chloride diffusion testing was performed on 12 SCM concrete mixtures cured in air, with a curing compound, or under continuous wet curing for 28 days, 91 days, and 180 days. The ternary mixtures interacted synergistically, reducing diffusivity at greater rates than binary SCM mixtures. The chloride diffusion coefficients of specimens cured outdoors were six times greater than for wet-cured specimens and the application of curing compound did not result in significant diffusivity reductions. Experimental data were compared to service-life-modeling software predictions for the experimental mixtures and showed that current software service-life predictions correspond to worst-case curing conditions.

An experimental program was carried out to characterize the risk of corrosion in reinforced concretes designed with alternative cementitious materials (ACMs). The study focuses on three alternative cementitious materials used with ordinary portland cement: glass powder (GP) obtained from mixture glass, alternative fly ash (AFA) obtained from the combustion of wastepaper deinking sludge and wood residues in a fluidized-bed reactor, and limestone filler (LF). Concrete specimens casted with water-binder ratios (w/b) of 0.4 and 0.55 were tested to determine compressive strength, chloride ion penetration, chloride diffusion, and porosity accessible to water. Reinforced concretes were also submitted to accelerated corrosion tests. The use of GP in replacement of cement increases resistance to chloride ion penetration. In this case, a low level of chloride ion penetration is maintained despite the increase of w/b. Hence, measurements of chloride ion penetration do not correlate with compressive strength values. The AFA improves resistance to the chloride ion penetration, particularly at high w/b, while the use of limestone filler has no significant impact. The chloride ion penetration tests show a good relation with the accelerated corrosion tests.