Expansive Admixture Research Articles

Effect of CaO on the shrinkage and microstructure of alkali-activated slag/fly ash microsphere

Alkali-activated materials (AAMs) are regarded as promising alternatives to Portland cement. However, the significant high shrinkage of AAMs, particularly in alkali-activated slag system, is a critical issue that hinders their wide application. This study investigated the effect of expansive admixture, i.e. CaO on the autogenous shrinkage and drying shrinkage of alkali-activated slag/ fly ash microsphere (AASFAM). The effect of CaO content on heat evolution, reaction products, microstructure development and compressive strength was systematically investigated. The results revealed that the addition of CaO can effectively reduce both the autogenous and drying shrinkage of AASFAM. Mixture with 3% and 5% CaO exhibited expansion within the first 24 hours after casting, while the drying shrinkage was reduced by 72% and 82%, respectively. The addition of CaO promoted the formation of crystalline phases including Ca(OH)2, hydrotalcite and calcite, leading to a lower free water content and coarser pore structure, which in turn reduced the capillary stress during the drying process. The results demonstrated the promising potential of CaO in effectively mitigating the high autogenous shrinkage and drying shrinkage of AAMs without compromising its mechanical properties.

Mock-up performance evaluation study for crack reduction of blast furnace slag powder concrete mixed with expansive and swelling admixtures

In this study, the drying shrinkage and crack reduction characteristics of blast furnace slag concrete mixed with expansive and swelling admixtures were investigated. Basic performance experiments were conducted using different mixtures of ground granulated blast-furnace slag (GGBS), with calcium sulfoaluminate as the expansive admixture and bentonite and hydroxypropyl methyl cellulose (HPMC) as swelling admixtures. Bentonite outperformed HPMC as a swelling admixture. Specimens were then prepared for mock-up tests to evaluate the drying shrinkage of blast furnace slag concrete with different combinations of bentonite, a hardening accelerator, and a self-healing agent. The addition of bentonite and calcium phosphate as a self-healing agent in small quantities reduced the drying shrinkage of the specimens, thereby reducing cracks. The cement mixture composed of 30% GGBS, 1% bentonite, and 1% calcium phosphate (30-E1-I1) showed the optimal performance among the specimens. Further, crack monitoring was performed in concrete made with ordinary Portland cement and optimal mixture 30-E1-I1. No cracks were observed for the optimal mixture. This shows that GGBS concrete can be used in practical and field applications, subject to mid- and long-term tests for cracking.

Investigation on hydration behavior and microscopic pore structure of early-age cement-based grouting material

The present paper reports an experimental investigation into the hydration behavior and microscopic pore structure evolution of early-age cement-based grouting material (CGM) with the same compressive strength as concrete (C60) at various ages (18 h, 1 d, 3 d, 7 d, and 28 d). The hydration process, hydration products, microstructure, and pore structure changes of early-age CGM were analyzed using isothermal calorimetry, thermogravimetry (TG), X-ray diffraction (XRD), backscattered electron imaging (BSEI), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP). The results show that the hydration process of early-age CGM can be classified into five stages: pre-induction, induction, acceleration, deceleration, and stabilization. Compared to C60, early-age CGM displays a higher initial heat flow but lower subsequent heat flow, with a cumulative heat release (72 h) only 38 % of that of C60, effectively avoiding temperature shrinkage and ettringite decomposition. During the hydration process, CGM continuously generates portlandite along with substantial quantities of ettringite and calcite. The addition of calcium sulphoaluminate expansive admixture (CSA) is advantageous in facilitating CGM's hydration process, effectively promoting the formation of ettringite and C–S–H gel, thus leading to an enhancement in the microstructure of CGM. At 28 d, the microstructure of CGM displays a relatively compact morphology. The porosity of CGM at 28 d was 13.74 %, with a higher proportion of harmless and less-harmful pores. These research findings contribute to a better understanding of the hydration process and microscopic pore structure evolution of early-age CGM, providing a reliable theoretical basis for the rational application of CGM in engineering and guidance for the improvement and optimization of CGM.

Design-oriented method for concrete pavements with volumetric stability admixtures: An integrated experimental and analytical approach

The high-performance demands on industrial floors, both in terms of larger slab dimensions and increased durability under harsh operating conditions, have led to the growing use of expansive admixtures. These generate a controlled expansive reaction within the concrete and compensate the early-age shrinkage. Despite their increasing use, calculation methods that permit to consider the expansive agents during the pavement design phase with a certain level of reliability are still unexistent. This study presents a straightforward cross-sectional model to assess both the stress-strain state and joint-opening of concrete pavements with volumetric stability admixtures by considering the slab dimensions, concrete composition, exposure conditions, and base friction characteristics. For that, a novel experimental device is designed and implemented in this work to characterize the dimensional variations associated with expansive agents since casting. A Type-G commercial volumetric stability admixture is considered as the expansive admixture. A full-scale validation of the proposed model is performed on a jointless concrete panel constructed by RCR Industrial Flooring in Spain. This validation proves the feasibility of the combined approach of laboratory calibration of the expansive addition and the cross-sectional model presented to accurately estimate both the slab deformations and joint opening developed over the 77-day test period.

Hydration properties of mixed cement containing ground-granulated blast-furnace slag and expansive admixture

Hydration properties of mixed cement containing ground-granulated blast-furnace slag and expansive admixture

Flexural behaviour of thin textile reinforced concrete slabs enhanced by chemical prestressing

Textile reinforcement gains recently increasing attention within the civil engineering field, especially for thin concrete elements such as facade slabs. Chemical prestressing, a method of inducing stresses using concrete with expansive admixtures, is an approach to enhance the performance of such slabs and allow for the better cracking behaviour and higher utilization of material properties of the textile reinforcement. This method was applied for thin slabs with epoxy impregnated carbon textile reinforcement. The slabs were investigated in four point bending tests and their cracking pattern was analysed with distributed fibre optic sensors and digital image correlation method. Chemical prestress positively influenced the load at initial crack formation and the corresponding deflection.

Population genetic structure of raccoons as a consequence of multiple introductions and range expansion in the Boso Peninsula, Japan

The raccoon (Procyon lotor) is an invasive carnivore that invaded various areas of the world. Although controlling feral raccoon populations is important to reduce serious threats to local ecosystems, raccoons are not under rigid population control in Europe and Japan. We examined the D-loop and nuclear microsatellite regions to identify spatially explicit and feasible management units for effective population control and further range expansion retardation. Through the identification of five mitochondrial DNA haplotypes and three nuclear genetic groups, we identified at least three independent introductions, range expansion, and subsequent genetic admixture in the Boso Peninsula. The management unit considered that two were appropriate because two populations have already genetic exchange. Furthermore, when taking management, we think that it is important to monitor DNA at the same time as capture measures for feasible management. This makes it possible to determine whether there is a invasion that has a significant impact on population growth from out of the unit, and enables adaptive management.

Autogenous Healing of Cracked Mortar Using Modified Steady-State Migration Test against Chloride Penetration

Concrete is a popular building material all over the world, but because of different physiochemical processes, it is susceptible to crack development. One of the primary deterioration processes of reinforced concrete buildings is corrosion of steel bars within the concrete through these cracks. In this regard, a self-healing technique for crack repair would be the best solution to reduce the penetration of chloride ions inside concrete mass. In this study, a rapid chloride migration (RCM) test was conducted to determine the self-healing capacity of cracked mortar. With the help of the RCM test, the steady-state migration coefficient of cracked and uncracked specimens incorporating expansive and crystalline admixtures was calculated. Based on the rate of change of the chloride ion concentrations in the steady-state condition, the migration coefficient was calculated. Furthermore, bulk electrical conductivity tests were also conducted before and after the migration test to understand the self-healing behavior. It was evident from the test results that the self-healing of cracks was helpful to reduce the penetration of chloride ions and that it enhanced the ability of cracked mortar to restrict the chloride ingress. Using this test method, the self-healing capacity of the new self-healing technologies can be evaluated. The RCM test can be an acceptable technique to assess the self-healing ability of cement-based materials in a very short period, and the self-healing capacity can be characterized in terms of the decrease of chloride migration coefficients.

Shrinkage Mitigation of an Ultra-High Performance Concrete Submitted to Various Mixing and Curing Conditions.

Ultra-High Performance Concretes (UHPC) are cement-based materials with a very low water-to-binder ratio that present a very-high compressive strength, high tensile strength and ductility as well as excellent durability, making them very interesting for various civil engineering applications. However, one drawback of UHPC is their pretty high autogenous shrinkage stemming from their very low water-to-binder ratio. There are several options to reduce UHPC shrinkage, such as the use of fibers (steel fibers, polypropylene fibers, wollastonite microfibers), shrinkage-reducing admixtures (SRA), expansive admixtures (EA), saturated lightweight aggregates (SLWA) and superabsorbent polymers (SAP). Other factors related to curing conditions, such as humidity and temperature, also affect the shrinkage of UHPC. The aim of this paper is to investigate the impact of various SRA, different mixing and curing conditions (low to moderate mixing temperatures, moderate to high relative humidity and water immersion) as well as different curing starting times and durations on the shrinkage of UHPC. The major importance of the initial mixing and curing conditions has been clearly demonstrated. It was shown that the shrinkage of the UHPC was reduced by more than 20% at early-age and long-term when the fresh UHPC temperature was closer to 20 °C. In addition, curing by water immersion led to drastic reductions in shrinkage of up to 65% and 30% at early-age and long-term, respectively, in comparison to a 20% reduction for fog curing at early-age. Finally, utilization of a liquid polyol-based SRA allowed for reductions of 69% and 63% of early-age and long-term shrinkages, respectively, while a powder polyol-based SRA provided a decrease of 47% and 35%, respectively.

Rheological behavior of low shrinkage very high strength self-compacting concrete

High performance self-compacting concretes have high potential to develop shrinkage, and possible solutions for this comportment should not compromise the workability of the mixtures. This work investigated rheological behavior over time of high performance self-compacting concretes (HPSCCs) containing an expansive admixture (EXA) and a shrinkage-reducing admixture (SRA). Cement pastes formulated from these HPSCCs were produced. The flow behavior of the HPSCCs and pastes were evaluated by rheometry and workability tests for up to 90 min. Isothermal calorimetry was utilized to measure the effect of EXA and SRA on cement hydration. The results showed that cement pastes containing SRA required less superplasticizer than pastes containing EXA and reference mixture, for the same workability. The flow behavior of cement pastes was similar at 90 min, independent of the rheological model adopted (Herschel-Bulkley or Bingham). The dynamic yield stress values of pastes containing some shrinkage mitigator agent ranged from 143 to 233 Pa at 90 min. The mixtures containing EXA showed an accelerated hydration, while incorporation of SRA in the pastes resulted in a retarded hydration of Portland cement compared to the reference mixture. After 90 min, by the slump flow diameter, all concretes could still be considered as self-compacting. The highest flow loss (−19.1%) was observed for concrete containing 15% EXA and the lowest (−0.1%) for the concretes containing 0.5% and 1.0% of SRA. After 90 min, the dynamic yield stress values of HPSCCs ranged from 19.5 to 40.7 Pa. Overall, shrinkage mitigator agents can be used in HPSCCs without compromising the workability of the mixtures.

New methodology to analyze the steel–concrete bond in CFST filled with lightweight and conventional concrete

The construction sector is constantly seeking for new building systems that are cheaper, faster and with a reduced generation of residues. In this way, the use of concrete-filled steel tubes (CFST) increased due to its fast and clean execution, and its high mechanical strength, durability and ductility. The performance of this system depends on the steel–concrete interaction that occurs in the form of a natural bond. The present work evaluates the natural bond mechanisms manifested in thin-walled steel tubes filled with three types of concrete: conventional, lightweight and lightweight with expansive admixture. Push-out tests were realized in the CFSTs and the results were compared with bond strength values prescribed by international standards. Finally, the residual concrete adhered to the CFST interface was evaluated by a new methodology using visual resources. Results indicated that the lower modulus of elasticity of the lightweight concretes contribute to the enhancement of the confinement effect and microlocking. And the expansive admixture improved the adhesion performance of the filling core. Additionally, the new methodology presents a good correlation with the other tests and it is easy to apply.

Effects of two admixtures on the axial compression of concrete-filled fibreglass tubes

This paper reports on an investigation into the influence of an expansive admixture (EA) and fly ash (FA) on the axial compressive behaviour of concrete-filled glass-fibre-reinforced polymer (GFRP) tube columns. The effect of EA and FA on the compressive strength and restrained expansion ratio was studied for two concrete strength grades, and optimised mixtures of expansive FA concrete were selected. It was found that the desired concrete strength and maximum expansion was obtained with 12% substitution of EA and 10% substitution of FA. For this study, 12 concrete-filled GFRP tube columns of circular cross-section were designed and fabricated considering parameters including the GFRP tube thickness, EA content, FA dosage and concrete strength. Their axial compressive behaviour was investigated through their failure modes, load-carrying capacity, ultimate stress and stress–strain curves. The results showed that increases in the thickness of the GFRP tube and EA content can enhance the axial compressive strength of concrete-filled GFRP tube columns. The theoretical ultimate load results showed good agreement with the experimental data.

Evaluation of Self-Healing in Concrete by Means of Analytical Techniques

In the present work, the self-healing process in concrete was evaluated using analytical techniques. For this purpose, two concrete mixes of different composition (one used as control) were prepared with a water-to-binder ratio of 0.45. The self-healing process was triggered by the introduction in the concrete mix of a commercial expansive admixture (calcium sulfo-aluminate), two dicarboxylic acids, and sodium carbonate salt. After 28 days curing in water, the specimens were artificially cracked (crack width ≤ 900 μm) and then again water-cured for further 60 days until self-healing occurred. The progress of self-healing was investigated with a stereomicroscope at 40, 50, and 60 days, after cracking, to identify the quality and the degree of the healing. The efficiency of the self-healing process was also evaluated using micro-Raman spectroscopy and X-ray micro-computed tomography. Significant reduction in the crack width was observed as a result of a calcite filling, generated during the self-healing process. In some cases (crack width < 400 μm), the crack was completely healed. The experimental methodology used provided new insights into the evolution of the self-healing phenomenon in concrete.

Experimental Study on Freezing and Thawing Cycles of Shrinkage-Compensating Concrete with Double Expansive Agents.

The freezing and thawing of construction concrete is becoming an increasingly important structural challenge. In this study, a shrinkage-compensating concrete based on a double expansive admixture was developed and its frost resistance was assessed through rapid freezing and thawing cycling. The frost resistance of the concrete was derived through the measurement and calculation of the relative dynamic modulus of elasticity (RDME) and the mass loss rate (MLR), and the freezing- and thawing-cycle microstructures and products of concretes with different expansive agents were analyzed using scanning electron microscopy (SEM). It was shown that changes in the properties of the concrete under freezing and thawing could be divided into three stages: slow-damage stage, fast-damage stage, and stable stage. Compared to concrete without an expansive agent, a single-expansive-agent concrete demonstrated excellent frost resistance during the slow-damage stage, but the frost resistance rapidly decreased during the fast-damage age. After 150 cycles (the stable-damage stage), the concrete with a U-type expansive agent (UEA): MgO expansive agent (MEA) mix proportion of 2:1 had the best frost resistance, with RDME and MLR values 17.35% higher and 25.1% lower respectively, than that of an expansive-agent-free concrete. These test results provide a basis for the study of frost resistance in large-scale hydraulic concrete structures.

Shrinkage-reducing measures and mechanisms analysis for alkali-activated coal gangue-slag mortar at room temperature

By using slag as a calcium source, high-strength alkali-activated coal gangue-slag (AACGS) cementitious material can be prepared. Given that higher drying shrinkage at room temperature is detrimental to the expanded engineering application of the material, this paper studies several methods for reducing drying shrinkage such as shrinkage-reducing admixture (SRA), polypropylene fiber (PPF), sulfate-enriched materials (gypsum, high-performance concrete expansive admixture (HCSA), U-type expansive admixture (UEA)) and water retaining admixture (WRA). Meanwhile, the mechanisms for drying shrinkage compensation were deeply analyzed by mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). Experimental results show that the addition of admixtures to reduce the drying shrinkage of AACGS mortar is related to the change of pore size of 2–5 nm, and reduces the volume fraction of the minimum aperture. At room temperature, reducing the surface tension of pore solution, generating expansion products, increasing compressive strength and improving pore structure distribution by adding admixtures are important measures to reduce drying shrinkage. SRA exhibits the strongest capacity to compensate for drying shrinkage, followed by UEA, WRA, HCSA, PPF and gypsum. Despite better compensation for drying shrinkage with the increase in SRA dosage, the reduction of strength value becomes more drastic. The findings of this study provide substantial experimental foundations and in-depth theoretical analyses for the drying shrinkage compensation of AACGS binary cementitious materials.

Experimental study on interior relative humidity development in early-age concrete mixed with shrinkage-reducing and expansive admixtures

Early age concrete may crack due to volumetric shrinkage caused by a decrease in the interior relative humidity (RH) in the self-desiccation process. Shrinkage-reducing admixtures (SRAs) and expansive admixtures (EAs) are utilized to mitigate the volumetric shrinkage. Using a self-developed wireless and automatic relative-humidity monitoring system, a series of experiments for the measurement of the RH within concrete specimens was conducted. A systematic analysis was conducted in the aspects of the setting time, critical time and interior RH development in early-age concrete with different dosages of the polymer-type SRA and CaO-type EA. On the basis, a critical time model and a two-stage RH development model considering the effects of the water to binder ratio, SRA and EA dosages were established. Both of the models are in good agreement with the experimental data.

Synergistic Benefits of Using Expansive and Shrinkage Reducing Admixture on High-Performance Concrete.

High-performance concrete (HPC) is widely used in construction according to great mechanical properties, but it has a high risk of shrinkage cracking due to autogenous shrinkage stress. Therefore, the aim of this research was to investigate the effect of a combination of expansive admixture (EA) and shrinkage reducing admixture (SA) on the autogenous shrinkage of high-performance concrete without heat treatment. Two different EA to cement weight ratios of 0.0, 5.0%, and two different SA to cement weight ratios of 0.0, and 1.0% were combined and considered. To investigate the differences in the time-zero conditions effect on the autogenous shrinkage behaviors, four different initial points were compared. The test results indicate that the EA and/or SA content was conductive to a little bite increase compressive strength (22.6–37.9%) and tensile strength (<4.8%). According to the synergistic effect of the EA and SA on the HPC, the autogenous shrinkage significantly decreased (<50%), as compared to those specimens with only one type of admixture (EA or SA). Furthermore, all the specimens incurred restrained autogenous shrinkage cracks at an early age, except the specimen using the combined EA and SA. Therefore, it can be concluded that the combination of EA and SA is effective for improving the properties of HPC.

Analysis of the Properties of Expansive Concrete With Portland and Blast Furnace Cement

AbstractThe properties of expansive concretes made of two types of cement: Portland cement CEM I and blast furnace slag cement CEM III were tested. The expansion of the concrete was caused by using an expansive admixture containing aluminium powder added in an amount of 0.5; 1 and 1.5% of cement mass. It was found that the compressive strength of concrete with CEM I decreased after using an expansive admixture in the amount of more than 0.5% of the cement mass. The compressive strength of concrete with CEM III decrease after addition of admixture in the entire range of dosages used. On the basis of electrochemical measurements, it was found no influence of an expansive admixture on corrosion of reinforcing steel. The use of an expansive admixture causes a slight increase in the effective diffusion coefficient of chloride ions in concrete.

Fresh properties of HPSCC containing SRA and expansive admixtures

Shrinkage-reducing admixture (SRA) and expansive admixture (EXA) were used in high performance selfcompacting concrete (HPSCC) to mitigate autogenous shrinkage. In order to evaluate the fresh properties of concretes, the rheological parameters were determined in a ICAR rheometer at 10, 25, 40, 60 and 90 min. The flow behavior of the mixtures was described by Bingham, Herschel-Bulkley, and modified Bingham models. Slump flow test, V-funnel test and J-Ring test were also carried out at 10 min. Slump flow test was performed also after 90 min of mixing. The test results showed that, at 10 minutes, all mixtures had similar performances, independently of the SRA and EXA contents. However, the slump flow test shows a reduction of up to 24% of its diameter at 90 min for mixtures with EXA. Mixtures with EXA revealed a gradual increase in dynamic yield stress with elapsed time. In contrast, concretes with SRA exhibited less variation in its rheological properties. Statistical analysis (ANOVA) showed that, regardless of the rheological model adopted, the admixture content was not a significant factor for the yield stress, while the type of admixture and the time of testing greatly influenced the concretes rheological response. Keywords: Shrinkage-reducing admixture (SRA), expansive admixture (EXA), rheological behavior, high performance self-compacting concrete.

A new approach for the mix design of (patch) repair mortars

The failure of most repairs in concrete structures is mainly manifested in the form of cracking and/or debonding of the repair layer. These two repair mechanisms could lead to the continuous corrosion of reinforcing steel in concrete. Cracking and debonding have been attributed to the high differential shrinkage that exists between the concrete substrate and repair layer as well as the lack of adherence, which commonly results from poor workmanship. It is crucial that restrained shrinkage mechanisms of patch repairs be understood so that the abovementioned effects can be prevented. The performance of patch repairs can be improved through the optimization of their mix design. Thus, it is common to use admixtures, non-cementitious compounds and polymers. However, promising technologies such as expansive admixtures that counteract shrinkage have found little application to date.Polymers do not chemically react with the cementitious matrix. They, however, have been reported to modify the microstructure in cementitious materials, consequently, resulting in improved properties with respect to mechanical, chemical and durability aspects. They increase chemical interactions with mineral phases, which improves the bond between the mortar and the substrate. Besides this, expansive cements are types of cement whose volume increases, unlike plain Portland cement where the volume typically decreases with time. This property relates to the use of expansive admixtures like quicklime, which exhibits an enormous volume increase upon hydration. This property leads to the reduction of the shrinkage, which is increased by the combination of the quicklime to a shrinkage-reducing admixtures (SRA).Using polymer technology and expansive admixtures, it is possible to develop a new approach for the mix design of repair mortars that combines the positive effects of polymer latex (increasing of bond strength) and expansive admixture (reducing the shrinkage) properties to reduce cracking and debonding failures in patch repairs.