Non-reactive Aggregate Research Articles

Effect of reactive coarse recycled aggregate with different expansion history on alkali silica reactivity and mechanical properties of new concrete

AbstractRecycled concrete aggregates (RCA) provide an environmentally friendly solution by reducing the depletion of natural resources. This study investigates the impact of the expansion history of RCA on its reactivity with alkalis in newly produced concrete. Parent concrete samples were collected from the RILEM AAR‐4 curing cabinet (60°C and >90% RH) to produce coarse RCA with four different expansion levels (0.00%, 0.05%, 0.12%, and 0.20%). The results show that the expansion levels of the new concrete mixtures decreased as the ASR expansion history of parent concrete increased. The 20‐week compressive strength and elastic modulus of the reactive aggregate concrete containing no mineral admixture and exposed to AAR‐4 test conditions were lower than those of their water‐cured counterparts. However, no decrease was observed in the elastic modulus of concrete mixtures that showed an expansion level lower than 0.03% (the maximum expansion for nonreactive aggregate as recommended by the RILEM AAR‐4 standard).

Evaluation of detrimental effects in concrete specimens due to the oxidation of sulfide-bearing aggregates after electrochemical treatment

Sulfide-bearing aggregates can cause significant damage when concrete has been produced without considering their potential deleterious oxidation reactivity. This study aims to find a reliable quantitative approach for assessing the impact of the harmful reaction of sulfide minerals (essentially pyrrhotite) in concrete specimens produced under laboratory conditions. To achieve this objective, different parameters such as an electrochemical treatment have been applied over 14, 28, 35 and 56-day periods on a series of concrete specimens made in the laboratory with a reactive sulfide-bearing aggregate (MSK 0.9) and non-reactive aggregate (PKA) After the treatment, the concrete specimens were tested with different tools such as non-destructive (Ultrasonic Pulse Velocity), semi destructive (expansion, modulus of elasticity and stiffness damage test) and destructive (concrete polished section and compression) methods to evaluate the impact of the deleterious reaction of the sulfide-bearing aggregates. The results show that concrete with the reactive aggregate can lose a significant amount of its mechanical performance exhibited principally by a significant reduction in modulus of elasticity (decreasing around 28% after 35 days of electrochemical treatment). Signs of damage associated with the use of the MSK aggregate were identified within concrete polished sections and under the SEM, which allowed to better describe the mechanisms of the oxidation reaction of the sulfide minerals. Ideal parameters/conditions can be achieved to evaluate the potential oxidation reaction of sulfide-bearing aggregates using the electrochemical treatment and the reduction of the modulus of elasticity of the concrete in a reasonable period of time.

ASR induced by chloride- and formate-based deicers in concrete with non-reactive aggregates

Despite ongoing efforts to prevent the damaging effects of alkali-silica reaction (ASR) in concrete structures, this phenomenon still exists and causes significant degradation. This study aims to investigate the role of various deicing agents in provoking ASR by examining volume expansion, cracks, and microstructure of mortar and concrete containing aggregates identified as non-reactive by standard ASR test methods. To achieve this, the concrete specimens undergo simulated operating conditions testing to induce ASR expansion, with an external supply of alkali from chloride- and formate-based deicers. The findings suggest that the configuration and concentration of the deicing agent used, as well as the mineral composition of the aggregate that was previously identified as non-reactive, can significantly impact the expansion and damage caused by ASR. The results indicate that existing methods for testing aggregates for ASR may have limitations when formate-based agents are used.

Long-term ultrasonic monitoring of concrete affected by alkali-silica reaction

This article presents continuous monitoring results of alkali-silica reaction (ASR) development in concrete specimens for over 400 days using ultrasonic testing and expansion measurements. Eight concrete specimens with nonreactive aggregate (Control), reactive coarse aggregate, and reactive fine aggregates were cast with two reinforced confinement conditions. The specimens were conditioned in an environmental chamber with high temperature and humidity (38°C and 90% relative humidity) to accelerate the ASR development. A multichannel ultrasonic monitoring system was developed to collect ultrasonic signals automatically, and the expansions in three directions were measured periodically. Results showed that the relative velocity change could detect the ASR initiation in all reactive specimens and show a correlation with expansion in the early stage. However, these correlations are inconsistent for different ASR specimens, and the velocity change becomes less sensitive to ASR damage in the late stage (after 300 days). Irrecoverable velocity drop was observed during every chamber shutdown period, especially in specimens with higher levels of ASR damage. This phenomenon suggests that the nonlinear ultrasonic response caused by the ambient temperature variation may indicate the ASR damage.

Effect of different fibres in mitigation of alkali-silica reaction

Alkali-silica reaction (ASR) is a phenomenon that causes irreversible damage to concrete structures. Since 1940, research has continued to investigate the possibility of eliminating these negative effects. The lack of availability of non-reactive aggregates requires the use of reactive aggregates, characterized by satisfactory physical and mechanical properties, with the introduction of innovative solutions to mitigate the effects of ASR expansion. Recently, fibre-reinforcement has shown to be a promising approach, even if the type and the volume of fibres used to reduce, or eliminate, the deleterious effects of expansion are not well established. For this reason, Miniature Concrete Prism Tests (MCPT) were performed on 4 series of expansive concrete prisms without any fibres and with 0.5% in volume of polypropylene fibres, steel fibres, and recycled carbon fibres, respectively. In addition, 4 series of non-expansive mortar prisms, with and without fibres, were tested in bending. As a result, by using recycled carbon fibres a moderate expansion can be observed after 56 days, in contrast to the high expansion of un-reinforced concrete. The same positive effect cannot be observed in concrete reinforced with steel or polypropylene fibres. This is due to the absence of the deflection hardening capacity of the fibre-reinforcement, as confirmed by both mechanical tests on non-expansive mortars, and by the analysis of microstructure on the post-mortem specimens.

Thermally Stable Redox Noninnocent Bathocuproine-Iron Complex for Cycloaddition Reactions

In this work, we aim to formally design iron(0) complexes combined with a phenanthroline-type ligand (phen) and investigate their utility in cycloaddition catalysis. Owing to the strong noninnocence of the phen scaffold, its ligation to reduced iron oxidation states classically affords particularly unstable species. The reported examples of such well-defined coordination complexes are thus particularly scarce. We demonstrate herein that a strategic steric protection of the C4 and C7 positions of the phen ring leads to neutral (N,N)2Fe species, which exhibits an unprecedented thermal and kinetic stability, amenable to its easy use as an in situ generated precursor in catalytic processes. The electronic structure of this noninnocent complex has been fully rationalized, and its promising catalytic activity in alkyne [2 + 2 + 2] cyclizations is discussed. Given its intrinsic thermal stability due to the noninnocent behavior of the (N,N) ligand, (N,N)2Fe appears to be an efficient dormant state of the catalytic process, precluding deactivation of iron as nonreactive aggregates.

Alkali–Silica Reactivity Potential of Reactive and Non-Reactive Aggregates under Various Exposure Conditions for Sustainable Construction

The alkali–silica reaction (ASR) is a primary cause for premature concrete degradation. An accelerated mortar bar test is often used to access the detrimental phenomena in concrete caused by the ASR of aggregates. However, this test requires a certain environmental conditioning as per ASTM C1260. The objective of this study is to explore the effects of the cement alkali content, exposure solution concentration, temperature, and test duration on mortar bar expansion. Factorial experimental design and analysis was conducted to delineate the effects of the individual factors as well as their interaction. Five different aggregates with various mineralogical properties were used, representing reactive and non-reactive aggregates. Various dosages of cement alkalis (0.40, 0.80, and 1.20 Na2Oe), sodium hydroxide (NaOH) solution concentrations (0.5, 1.0, and 1.5 N), and temperature (40 °C, 80 °C, and 100 °C) were the studied variables. Mortar bar expansion was measured at 3, 7, 14, 21, 28, 56, and 90 days. Mortar bars incorporating Jhelum aggregates incurred expansion of 0.32% at 28 days, proving to be reactive aggregates as per ASTM C1260. Similarly, specimens incorporating Taxila aggregates showed expansion of 0.10% at 28 days, indicating non-reactive nature. It was observed that specimens with Sargodha aggregates showed expansion of 0.27% at 28 days for 0.50 N NaOH solution concentration compared to 0.31% expansion for identical specimens exposed to 1.5 N solution. Moreover, expansion increased with exposure duration for all the tested specimens. Experimental results showed that the cement alkali contents had relatively lesser effect on expansion for 1.0 N NaOH; while, in the case of 0.5 N and 1.5 N NaOH, the cement alkali had a significant effect. It was noted that expansion increased with an increase in the temperature. Jhelum aggregates showed 28-day expansion of 0.290% when exposed to 40 °C, but at a temperature of 100 °C, expansion increased to 0.339%. Factorial analysis revealed that the exposure solution had a major contribution towards the expansion of mortar bar specimens. This study highlights the contribution of various exposure conditions on the ASR expansion, which leads to a decisive role in selecting the aggregate sources for various applications and exposure conditions leading to sustainable construction.

Optimization of Parameters of the New Turner-Fairbank Alkali-Silica Reactivity Susceptibility Test (T-Fast)

Abstract Prevention is an effective strategy to avoid damage caused by the alkali-silica reaction (ASR) in concrete structures. The effectiveness of this strategy heavily depends on the use of reliable accelerated tests to determine if an aggregate used in the concrete has the potential to cause ASR. Recently, a new provisional standard test, AASHTO TP 144-21, Determining the Potential Alkali–Silica Reactivity of Coarse Aggregates (TFHRC-TFAST), has been approved by the American Association of State Highway and Transportation Officials. The test accurately predicted the ASR-induced expansion of aggregates used in more than 50 different mortar and concrete samples, including concrete blocks in outdoor testing facilities and concrete in the field. This manuscript presents the results of the collaborative study among three laboratories conducted as part of an overall effort to standardize the new AASHTO TP 144-21. The objectives of the study were to evaluate the suitability of wavelength dispersive x-ray fluorescence (WDXRF) spectroscopy as the main analytical technique, determine the optimal particle size and effect of moisture on calcium oxide (CaO), and evaluate sample preparation on the results. A total of 18 aggregates were evaluated under the TP 144-21 using 4 different CaO samples and 2 sample preparation protocols. The results indicated that the alkali-silica reactivity of the aggregates can be accurately determined by using WDXRF. Upon exposure to the atmosphere, CaO reacts rapidly with moisture to produce calcium hydroxide [Ca(OH)2]. The particle size distribution and amount of Ca(OH)2 in the CaO influenced the ASR classification of marginal (moderately and slow reactive) and nonreactive aggregates. The researchers obtained optimal results using a reagent grade powder CaO with an average particle size of 4.6 μm and less than 5 % of Ca(OH)2. These conclusions were important to validate and optimize the TP 144-21 protocol before launching a wider interlaboratory study.

Use of Off-ASTM Class F Fly Ash and Waste Limestone Powder in Mortar Mixtures Containing Waste Glass Sand

Developing sustainable concrete with less ordinary Portland cement is a growing issue in the construction industry. Incorporating industrial by-products (such as fly ash or slag) or municipal solid wastes (such as waste glass or recycled concrete aggregate) into the concrete becomes an effective way to reduce the consumption of natural sources and carbon dioxide emission if a proper mix design is provided. The present study examines the influence of the combined use of off-ASTM Class F fly ash (FFA) and waste limestone powder (LSP) on flowability, compressive strength, and expansion characteristics of mortar mixtures containing waste glass sand (WGS). FFA and LSP were used as cement replacement while WGS was used as partial reactive siliceous river sand replacement. Material variables included different WGS replacement ratios (25%, 50%, and 75%) with river sand, LSP contents (25%, 50%, and 75%), FFA contents (15%, 30%, and 45%), and different combinations of FFA-LSP (15–10%, 15–15%, 15–30%, and 15–35%). It is shown that the single use of FFA or LSP reduces both compressive strength and flowability of mortar mixture as its replacement level increases. However, mixtures combined with FFA and LSP provide higher or comparable strength to the single LSP or FFA mixture. For the expansion characteristics due to alkali-silica reaction, the single-use of more than 30% FFA or 75% LSP has less than 0.1% expansion, which is a non-reactive aggregate criterion based on the C1260/C1567 when the test period is extended to 56 days. Moreover, the combination of FFA and LSP has a considerable reduction in expansion rate compared to the single FFA or LSP mixture.

Use of carbonated Portland cement clinkers as a reactive or non-reactive aggregate for the production of cement mortar

This study investigates the effects of carbonated cement clinker used as a fine aggregate on the strength and physicochemical properties of mortar. Cement clinkers in two different size ranges (0.15 mm–1.2 mm and 1.2 mm–5 mm) were replaced with natural fine aggregate. The cement clinkers were carbonated by natural and accelerated carbonation methods. The results demonstrated that the use of carbonated cement clinker has a positive effect on the strength properties of mortar. A physicochemical analysis showed that seven days of accelerated carbonation generated high levels of calcite on larger cement clinker aggregate materials (1.2 mm–5 mm). However, these higher amounts of carbonation products can detrimentally affect the creation of efficient bonding with the other ingredients in mortar and can consequently lower the strength of these materials compared to when smaller carbonated cement clinkers (0.15 mm–1.2 mm) are used in mortar. Fewer carbonation products provide additional nucleation sites for the hydration of cement grains. Therefore, relatively small carbonated cement clinker is preferable to large carbonated cement clinker to obtain high strength. The findings overall lead to the conclusion that carbonated cement clinker can be used as a reactive aggregate or non-reactive aggregate depending on the degree of carbonation. In both cases, the performance of cement mortar exceeds that of cement mortar containing natural sand.

Study and development of hardening mixture composition based on unconventional industrial waste

Relevance. Phosphogypsum, the product of apatites chemical processing, is one of the most common mining wastes. Phosphogypsum utilization is not widespread yet, therefore its cost is low. Integrated research has been carried out to determine the technological capacity and economic feasibility of phosphogypsum, sludge, and dolomite utilization as binders in the conversion of ore production techniques. Research aim is to develop a hardening mixture composition based on unconventional industrial waste, determine the technological capacity and economic feasibility of utilizing phosphogypsum, sludge, dolomite, and other accessible low activity wastes as a substitute for expensive and relatively scarce binder material. Research methodology. Initial data are studied of the wastes possessing binding properties. The efficiency of admixing them is determined from the robustness of hardening backfill mixtures control samples that have been produced in laboratory conditions. Based on the research, a database is created to apply the results in practice for mining development. Results. The hardening materials compositions were obtained based on unconventional industrial waste including hydrometallurgical and dressing tailings, furnace clinker, low-grade sand, thermal power plants (TPP) and chemical industry ashes. The optimal composition of the mixture per cubic meter: tailings – 600–750 kg; TPP ash – 180–220 kg; cement dust – 250–315 kg; cement – 35–40 kg; tempering water – 450–515 l under the mixture’s fluidity of about 14 cm according to the readings of the mortar consistency measuring device (StroyTsNIL cone). To ensure radiation safety of the hardening mixture that is based on unconventional industrial waste, it is advisable to take into account not only their chemical and physical-mechanical indicators but the value of naturally radioactive nuclides’ effective activity as well. Conclusions. It has been stated that the robustness of mixtures containing gypsum is 1.5–2.0 times higher, and under the hardening time of 3, 6 and 12 months makes up 3.1; 5.7 and 7.6 MPa correspondingly. It has been shown that the compositions with the binder’s flow rate of 450 kg per cubic meter under the cement : sludge ratio of 1 : 2 show the robustness from 2.8 to 4.9 MPa in 28 days. The content of low-grade sand levigate particles reaches 20% and more. Classes with a specific area of 28.4 m2/kg refer to fine sand, and with a specific area of 27.7 m2/kg refer to medium sand. The robustness of the 28 days old composition reaches 0.5 MPa, 90 days – 0.9 MPa depending on the cement flow rate. It has been substantiated that binders based on fluorine gypsum, phosphogypsum, and belite sludge by mixed grinding of the granulated 26 "Izvestiya vysshikh uchebnykh zavedenii. Gornyi zhurnal". No. 3. 2021 ISSN 0536-1028 blast-furnace slug with the ferrochrome sludge and phosphogypsum up to 70%, 0.08 mm size, show the robustness of the binder up to 3.0 MPa with the flow rate of 450 kg per a cubic meter of the mixture. Keywords: industrial waste; hardening mixture; binder; PPT ash; ash and slag; cement; fluorine gypsum; phosphogypsum; non-reactive aggregate; belite sludge; naturally radioactive nuclides. Acknowledgements. Specialists from Platov South-Russian State Polytechnic University (Novocherkassk, Russia), Ukrainian Research and Design Institute of Industrial Technology (Zhovti Vody, Ukraine), Vostochnyy (Eastern) Mining and Enrichment Combine (Zhovti Vody, Ukraine), Dnipro University of Technology (Dnipro, Ukraine) and others took part in creating, improving, and introducing R&D.

Materials Data Science for Microstructural Characterization of Archaeological Concrete

ABSTRACTAncient Roman concrete presents exceptional durability, low-carbon footprint, and interlocking minerals that add cohesion to the final composition. Understanding of the structural characteristics of these materials using X-ray tomography (XRT) is of paramount importance in the process of designing future materials with similar complex heterogeneous structures. We introduce Materials Data Science algorithms centered on image analysis of XRT that support inspection and quantification of microstructure from ancient Roman concrete samples. By using XRT imaging, we access properties of two concrete samples in terms of three different material phases as well as estimation of materials fraction, visualization of the porous network and density gradients. These samples present remarkable durability in comparison with the concrete using Portland cement and nonreactive aggregates. Internal structures and respective organization might be the key to construction durability as these samples come from ocean-submersed archeological findings dated from about two thousand years ago. These are preliminary results that highlight the advantages of using non-destructive 3D XRT combined with computer vision and machine learning methods for systematic characterization of complex and irreproducible materials such as archeological samples. One significant impact of this work is the ability to reduce the amount of data for several computations to be held at minimalistic computational infrastructure, near real-time, and potentially during beamtime while materials scientists are still at the imaging facilities.

Single-Impact Nonlinear Resonant Acoustic Spectroscopy for Monitoring the Progressive Alkali–Silica Reaction in Concrete

Alkali–silica reaction (ASR) is a ubiquitous cause of concrete degradation. The reaction produces an expandable gel that may cause internal over-stressing and cracking. This paper demonstrates the utility of single-impact nonlinear resonant acoustic spectroscopy (SINRAS) for monitoring the progress of ASR over the course of a standard ASR-susceptibility test. In SINRAS, the transient softening and subsequent recovery of resonance frequency due to one strong impact are analyzed. The performance of SINRAS in monitoring ASR is compared to that of multi-impact nonlinear resonant acoustic spectroscopy (MINRAS), where the gradual resonance frequency shifts caused by impacts of increasing intensity is measured. The changes in standard linear expansion and linear resonance frequency are recorded in parallel. Finally, the sensitivity of measured parameters to sample temperature is investigated. Our findings indicate that SINRAS, while being much simpler and faster to conduct, yields results that strongly correlate to those from MINRAS and even gives an additional parameter describing the rate of recovery. The extracted nonlinearity parameters exhibit good sensitivity and clearly differentiate between concrete with reactive and non-reactive aggregates. Further, this study suggests that the influence of sample temperature on the nonlinearity parameters depends on the level of ASR progression and has to be taken account.

Alkali-silica reactivity of alkali-activated concrete subjected to ASTM C 1293 and 1567 alkali-silica reactivity tests

This paper presents an experimental investigation of the alkali-silica reactivity of alkali-activated concrete (AAC). Some researchers suggest that the high alkalinity of the pore solution could make AAC more susceptible to alkali-silica reaction (ASR) than comparable ordinary Portland cement (OPC) concrete, perhaps even with aggregates that are normally considered non-reactive. Many have further questioned the suitability of standardized ASR test methods for use with AAC. In an attempt to resolve this controversy, the authors subjected OPC, alkali-activated fly ash (AAF), and alkali-activated slag (AAS) concrete made with both reactive and non-reactive aggregates to accelerated and long-term ASR test protocols (ASTM C1567 and C1293). Paradoxically, some AAS mixtures with non-reactive aggregates showed significant expansion while AAF mixtures with reactive aggregates expanded minimally. AAS mixtures with reactive aggregates underwent extremely high expansions. Microstructural evaluation using scanning electron microscopy revealed significant cracking but did not identify ASR gel in the majority of specimens.

Use of Contaminated Sand Blasting Grit for Production of Cement Mortars

The influence of the industrial waste on the surrounding environment has been under surveillance of researchers for many years. Various industrial wastes that need to be stored and disposed of can contaminate water and soil. One of the industrial wastes that has to be disposed is the sand blasting grit or sand blasting residue. Sand blasting is a process of removing outer layers, paint or rust from steel elements such as bridge lattice or warehouse frames. Safe disposal of waste products is costly and time consuming. The study analyses the suitability of contaminated sand blasting grit for production of cement mortars. The waste material was acquired from a local company and it was used as a non-reactive aggregate. The study focuses on the influence of the amount of the waste material on the rheological and strength properties of produced mortars. The sand blasting grit was added as a partial or full replacement of natural sand. Results of performed tests show a potential possibility of using the contaminated sand blasting grit for production of mortars. However, an increase in the overall amount of waste product in the mortars was followed a by decrease of the strength. The addition of the grit also decreased the flowability of the mortar. Use of contaminated sand blasting grit for production of mortars allows reduction of the high costs of waste disposal and storage.

Determination of Optimal Aggregate Blending to Prevent Alkali-Silica Reaction Using the Mixture Design Method

Abstract Alkali-silica reaction (ASR) can cause serious cracking in concrete. The best method in order to avoid the occurrence of ASR is the non-use of reactive aggregate in concrete production. However, reactive aggregates in quarries must be used for the sustainable usage of resources. Therefore, a more practical approach is to identify the optimal blending of such aggregates, which can be achieved through the use of the Design of Experiment-Mixture Design Method (DOE-MD). In this study, empirical approaches that can be used for ASR estimation are suggested using DOE-MD in a quarry that produces concrete aggregate and has reactive and nonreactive aggregate resources in terms of ASR and by determining aggregate mixing ratios that do not create risk in terms of ASR. The quarry in question has three different regions, which are in terms of the type of aggregate available. As a result, the aggregate from Region 2 should be used at 19 % (Region 3: 81 %) in the mixture with aggregate from Region 3. The aggregate from Region 1 should not be mixed with the aggregate from Region 2 and should be used at most at 14 % (Region 3: 86 %) in the mixture with the aggregate from Region 3.

Visualization of internal crack growth due to alkali–silica reaction using digital image correlation

This study visualized the development of micro-cracks in concrete due to the progression of the alkali–silica reaction (ASR) in two dimensions using a digital image correlation (DIC) technique. First, a preliminary experiment to determine the optimum specimen size for DIC was conducted on three specimens with different thicknesses. The results show that the ASR neither caused macro-level expansion nor attenuation of the ultrasonic propagation velocity in concrete specimens with a thickness of 10 mm. This was attributed to the leakage of the alkali–silica gel from the surface. On the other hand, we found that specimens with a thickness of 30 mm or greater were suitable for visualizing strain distributions on the concrete surface. Second, we examined the effects of the mechanical properties of aggregates on the ASR-induced crack propagation in concrete. The specimen dimensions were chosen based on the results of the preliminary experiment, and the mixing ratios selected ensured the manifestation of pessimum effects. The degree of concrete expansion depended on the type of non-reactive aggregate used in the mixture. Furthermore, the ASR-induced expansion of concrete was significantly reduced with the introduction of an artificial lightweight aggregate as the non-reactive aggregate, and the mechanical properties of the aggregate(s) were found to affect the ASR-induced crack growth.

Outdoor exposure site testing for preventing Alkali-Aggregate Reactivity in concrete – a review.

Alkali-silica reaction (ASR) is a deleterious chemical reaction affecting the durability and service life of concrete structures worldwide. Specifications and recommendations were produced in many countries to ensure that non-reactive aggregates are used in concrete construction or, when reactive aggregates must be used, appropriate preventive measures are implemented. Such recommendations, especially those related to the use of supplementary cementitious materials (SCM) to prevent ASR, are generally based on laboratory investigations, but preferably on field performance surveys of concrete structures where such measures have been implemented. Over the past 50 years, outdoor exposure sites have been developed in several countries with the objective of validating data obtained from laboratory testing for various combinations of reactive aggregates and SCM, as well as for determining long-term performance of specific mix designs. This paper reviews worldwide efforts regarding outdoor exposure site testing for ASR prevention.

Effect of alkali release by aggregates on alkali-silica reaction

Mortar and concrete specimens were made using one alkali-bearing reactive aggregate, one alkali-free reactive aggregate and one alkali-free non-reactive aggregate in order to determine the effect of an alkali release by an aggregate into the pore solution on the development of ASR using pore water extraction and direct expansion measurements. The fine fraction of the alkali-bearing reactive aggregate was found to be able to release up to 3wt% of its total Na2O content (0.73kgNa2O/m3) into the pore solution of mortar at the age of one year for specimens stored at 60°C. However, there is no evidence that this sodium release influenced the rate of the development of the expansion. Results on mortar specimens also indicated that the amount of Na2O bounded into ASR gel is approximately proportional to the progress of expansion. The same proportionality is however not observed for potassium ion. For concrete specimens, it is clear that Na2O and K2O ions are bound into ASR reaction products, but there is no evidence that the coarse fraction of the alkali-bearing aggregate released alkalis into the pore solution of concrete after one year of testing completed in this study.

Empirical Multiphase Dielectric Mixing Model for Cement-Based Materials Containing Alkali-Silica Reaction Gel

Alkali-silica reaction (ASR) is a common cause of concrete deterioration. Water (either in free or bound form), in the presence of reactive aggregates, plays a major role in the reaction itself and in the formation and expansion of the deleterious gel produced. Since microwave signals are sensitive to the presence of water in dielectric materials, microwave materials characterization techniques have the potential to detect and monitor ASR gel in concrete structures. Dielectric mixing models are physics-based models that relate the macroscopic (i.e., effective) dielectric constant of a material to the dielectric constant of its constituents and their respective volumetric contents. In this investigation, an empirical multiphase dielectric mixing model is developed in conjunction with measured dielectric constants of two sets of mortar samples with ASR-reactive and nonreactive aggregates at R-band (1.7–2.6 GHz). The proposed model is capable of closely predicting the effective (temporal) dielectric constant of the samples. The modeling results are validated by a comparison with the measured temporal dielectric constant of the samples, showing good agreement. Through this investigation, quantitative information on the influence of constituents of ASR-reactive mortar samples (including ASR gel) are obtained, and the pertinent results indicate significant potential for microwave materials characterization techniques for ASR detection and evaluation.