Internal Curing Agents Research Articles

Use of Zeolite as Both Internal Curing Agent and Supplementary Binder in Mortar

Use of Zeolite as Both Internal Curing Agent and Supplementary Binder in Mortar

Carbon nanofibers and polyvinyl-alcohol fiber hybrid-reinforced high-performance concrete: Mechanical property, chloride penetration resistance, and material characterization

The hybridization of nanomaterials and macroscopic fibers is currently a popular topic. The aim of this study was to explore the application potential of incorporating carbon nanofibers (CNFs) into concrete and to analyze the effect of CNFs dispersant on concrete slump and early strength. Polyvinyl alcohol (PVA) fibers and CNFs were used to prepare composite fiber-reinforced (CNFs-PVA) concrete to improve the continuity of concrete properties at the micron/nanometer scale. The engineering properties such as compressive strength, flexural strength and resistance to chloride ion erosion performance of the concrete were investigated, and the microstructure of concrete was characterized using X-ray diffraction (XRD), scanning-electron microscopy (SEM), and X-ray computed tomography (X-CT). The results showed that CNFs could improve the early strength. The combined use of CNFs and PVA increased the 28-day compressive and flexural strength by 23.38% and 28.73%, respectively, compared to the control group. Correspondingly, the electric flux and Migration rate of chloride ions (DRCM) were minimized. From the SEM and XRD test results, it is clear that CNFs and PVA fibers can: (i) bridge low-density C-S-H to form higher-density C-S-H gels, (ii) form longer chain-like fibers with enhanced load transfer and chloride binding capacity, (iii) act as internal curing agents to enhance hydration at the interface, (iv) promote the formation of the aluminum phase hydration products and calcium carbonate phase, and (v) CNFs and PVA refine the pore size by increasing the gel pores and reducing the percentage of microcracks. The combined results indicate that the improved performance of CNFs-PVA is due to the combined effect of bridging and nucleation of hydration products by CNFs, adsorption of hydration products by CNFs-PVA, and promotion of pore filling by the generated hydrides such as calcium carbonate and ettringite. These findings provide new insights for the design of high-performance concrete materials.

Anti-cracking concrete properties based on the synergistic expansion effect of internal curing agents

This paper designed 7 groups of C40 crack resistant concrete mix and conducted experimental research on working properties, mechanical properties, deformation properties and crack resistance, with monolithic laminated wallboard technology. The test results find that: the shrinkage compensated concrete with curing agent in light sand shows that the curing agent in light sand gives full play to the synergistic expansion effect. While significantly improving the design strength of concrete, it effectively controls the crack generation in the solidification process of concrete specimens, which has good crack resistance and durability. From the aspect of concrete mix design, this study provides an effective solution to control the cracks of cast-in-place concrete structures in the process of application of assembled monolithic laminated wallboard technology.

An Experimental Evaluation of Hemp as an Internal Curing Agent in Concrete Materials.

The construction industry is facing increased demand for adopting sustainable 'green' building materials to minimise the carbon footprint of the infrastructure sector to meet the United Nations 2030 Sustainability Goals. Natural bio-composite materials such as timber and bamboo have been widely used in construction for centuries. Hemp has also been used in different forms in the construction sector for decades for its thermal and acoustic insulation capability owing to its moisture buffering capacity and thermal conductivity. The current research aims to explore the possible application of hydrophilic hemp shives for assisting the internal curing of concrete materials as a biodegradable alternative to currently used chemical products. The properties of hemp have been assessed based on their water absorption and desorption properties associated with their characteristic sizes. It was observed that, in addition to its excellent moisture absorption capacity, hemp released most of its absorbed moisture into the surroundings under a high relative humidity (>93%); the best outcome was observed for smaller hemp particles (<2.36 mm). Furthermore, when compared to typical internal curing agents such as lightweight aggregates, hemp showed a similar behaviour in releasing its absorbed moisture to the surroundings indicating its potential application as a natural internal curing agent for concrete materials. An estimate of the volume of hemp shives required to provide a similar curing response to traditional internal curing techniques has been proposed.

Influence of cellulose micro-fibers on hydration characteristics of cementless UHPC using CaO-activated GGBFS

This study aimed to investigate the influence of natural cellulose fibers (NCFs) on improving the hydration characteristics of cementless ultra-high performance concrete (UHPC) using CaO-activated ground granulated blast furnace slag (GGBFS). The NCFs were added in a saturated condition as an internal-curing agent so as to supply additional water to the UHPC matrix and subsequently increase the reactivity of unhydrated phases. To evaluate the hydration characteristics, saturated NCFs were added at 0 to 1.5 wt% of the GGBFS plus CaO. TGA and FTIR analyses showed that, as the amount of NCFs increased, the formation of hydration products was improved as evidenced by an increase in heat of hydration, indicating that more reactions of unhydrated phases occurred. Similarly, morphologies of the samples revealed the formation of hydration products on and near the surfaces of the NCFs due to the additional water exerted during the process of internal curing. Moreover, the compressive and tensile strengths were not compromised by the incorporation of weak and flexible NCFs, but rather a slight improvement was observed with a certain content of NCFs.

Optimising internal curing parameters for autonomous curing of normal-strength concrete

Autogenous curing, also known as internal curing (IC), has revolutionised the way high-performance concrete (HPC) and high-strength concrete (HSC) are cured. IC improves the service life of concrete by lowering early-age cracking and enhancing durability. However, normal-strength concrete (NSC), the most commonly used type in the industry, is typically cured using conventional methods. Researchers are thus looking at ways to reproduce the positive results found in internally cured HSC/HPC in NSC. Studies have shown that IC is feasible in NSC despite its higher permeability, which results in loss of internal curing water (ICW). However, no comprehensive study has attempted to assess how the type, size and amount of IC agents affect the properties of NSC. The aim of this work was thus to optimise IC parameters for autonomous curing of NSC. The findings of this study support the notion that IC is possible in concrete with a high water/cement ratio and that, compared with lightweight aggregates (LWAs), superabsorbent polymers significantly impacted the durability properties of the NSC. Moreover, varying the size of the IC agent (LWA) had little effect on NSC properties, while increasing the amount of ICW considerably improved the durability properties.

Quantifying the water donation potential of commercial and corn starch hydrogels in a cementitious matrix

In this study, we introduce a new methodology to quantify the internal curing potential of hydrogels in a cementitious matrix. The swollen Super Absorbent Polymers (SAPs) and newly synthesized corn-starch hydrogels are investigated by embedding a capsule filled with swollen hydrogel in a cement mortar cube and monitoring the internal wetting area around the hydrogel capsule for 56 days. Our findings demonstrate that all of the investigated hydrogels serve as effective internal curing agents, releasing water in a cyclic pattern governed by the humidity gradient between the hydrogel and the surrounding matrix. Moreover, the regions around the hydrogel capsules display a denser accumulation of calcium silicate hydrate (CSH) gel, indicating improved hydration due to internal curing from the hydrogels. This research offers valuable understanding into the possibilities of utilizing bio-based materials and SAPs for internal curing and the creation of environmentally friendly cementitious materials. In summary, the proposed innovative approach serves as an effective way for measuring the internal curing capabilities of hydrogels within cementitious materials.

Influence of internal curing on compressive strength and drying shrinkage of super-sulfated cement mortar

The current study aims at assessing the effect of using cold-bonded fly ash based artificial lightweight aggregate (ALWA) as an internal curing (IC) agent on the compressive strength and drying shrinkage of a typical super-sulfated cement (SSC) produced with a mixture of 85% slag, 10% gypsum, and minor amount of 5% blended Portland cement (PCB). The ALWA was used as partial replacement of fine aggregate (FA) at values of 25, 50, 75, and 100 vol.%. Experimental results showed that the ALWA partially replacing FA in range of 25–100 vol.% significantly decreased both the unit weight and dried density of the fresh and hardened IC-SSC mortars at average values of 13.9% and 20.0%, when compared with the reference SSC mortar, respectively. The ALWA increment continuously reduced the compressive strengths of the hardened IC-SSC mortars. But, at 28 days of curing, the hardened IC-SSC mortar containing the ALWA amount partially replacing FA up to 50 vol.% showed compressive strength reaching 89.3%, and comparable or slightly lower drying shrinkage in comparison with the reference SSC mortar without the IC agent.

Utilization of artificial lightweight aggregate and unground rice husk ash as internal curing agents to modify performance of super-sulfated cement mortar

This study attempts to utilize cold-bonded fly ash based artificial lightweight aggregate (ALWA) and retrieved unground rice husk ash (URHA) as internal curing (IC) agents for improving performance of typical super-sulfaed cement (SSC) mortar fabricated with ternary mixture of 85% slag, 10% gypsum, and only 5% blended Portland cement (PCB). The ALWA partially replacing fine aggregate (FA) at four values of 25, 50, 75, and 100 vol.% was used. For evaluating impact of using hybrid addition of IC agents on performances of SSC mortars, the ALWA amount after being optimized was partially replaced by URHA at four levels of 25, 50, 75, and 100 vol.%. Experimental results showed that, ALWA partially replacing FA up to 50 vol.% led to the SSC mortars with remarkably increased workability and uncompromised impacts on the strengths and durability. Addition of URHA partially replacing ALWA significantly improved the fresh properties and flexural strength but it negatively impacted the durability performances of the resultant SSC mortars in terms of increased water absorption, decreased UPV, and increased drying shrinkage.

Toxicity assessment of core-shell and superabsorbent polymers in cell-based systems

The identification of health risks arising from occupational exposure to submicron/nanoscale materials is of particular interest and toxicological investigations designed to assess their hazardous properties can provide valuable insights. The core-shell polymers poly (methyl methacrylate)@poly (methacrylic acid-co-ethylene glycol dimethacrylate) [PMMA@P (MAA-co-EGDMA)] and poly (n-butyl methacrylate-co-ethylene glycol dimethacrylate)@poly (methyl methacrylate) [P (nBMA-co-EGDMA)@PMMA] could be utilized for the debonding of coatings and for the encapsulation and targeted delivery of various compounds. The hybrid superabsorbent core-shell polymers poly (methacrylic acid-co-ethylene glycol dimethacrylate)@silicon dioxide [P (MAA-co-EGDMA)@SiO2] could be utilized as internal curing agents in cementitious materials. Therefore, the characterization of their toxicological profile is essential to ensure their safety throughout manufacturing and the life cycle of the final products. Based on the above, the purpose of the present study was to assess the acute toxic effects of the above mentioned polymers on cell viability and on cellular redox state in EA. hy926 human endothelial cells and in RAW264.7 mouse macrophages. According to our results, the examined polymers did not cause any acute toxic effects on cell viability after any administration. However, the thorough evaluation of a panel of redox biomarkers revealed that they affected cellular redox state in a cell-specific manner. As regards EA. hy926 cells, the polymers disrupted redox homeostasis and promoted protein carbonylation. Concerning RAW264.7 cells, P (nBMA-co-EGDMA)@PMMA caused disturbances in redox equilibrium and special emphasis was placed on the triphasic dose-response effect detected in lipid peroxidation. Finally, P (MAA-co-EGDMA)@SiO2 activated cellular adaptive mechanisms in order to prevent from oxidative damage.

Evaluation of Aloe barbadensis Miller and Musa x paradisiaca as Internal Curing Agents in Concrete

Curing is essential for enhancing the durability and strength of concrete. Researchers found that a lack of conventional curing in earlier days leads to a loss of economy over the years after construction finishes. Self-curing concrete is a contemporary type of concrete that holds water, prevents loss of moisture from the surface, and facilitates self-curing. The existing chemical admixture for self-curing, polyethylene glycol (PEG), is expensive. Hence, in this research, bio admixtures such as Aloe barbadensis miller and Musa x paradisiaca were tried as self-curing agents and compared with the performance of PEG. The functional groups of such bio admixtures match with those of PEG. The results show that the fresh and hardened properties of M30 concrete are better than the conventionally cured concrete and PEG added to concrete. The optimized percentages of admixtures are 0.25% for Aloe barbadensis miller, 1% for Musa x paradisiacal, and 0.5% for PEG, improving the compressive strength by 23.3%, 1.7%, and 4.5%, respectively. Similarly, split tensile and flexural strength have been enhanced up to 4.24 MPa and 15.05 MPa for Aloe barbadensis miller, and 3.82 MPa and 13.65 MPa for Musa x paradisiacal. The characterization studies’, such as XRD (X-ray diffraction), SEM (scanning electron microscope), and EDX (energy dispersion analysis), results show the early formation of hydrated products, such as CSH and CH, after 7 days of curing with an optimized mix. Of the two plant extracts, Aloe barbadensis miller performed better than Musa x paradisiacal and water-cured concrete.

Investigating the effect of hybrid curing on mechanical and durability properties of normal-strength concrete

Internal curing is commonly implemented in concrete mixes with water-to-cement (w/c) ratios lower than 0.4 because of self-desiccation. Normal Strength Concrete (NSC) with w/c ratios higher than 0.5 would benefit from internal curing because of labor and resource-saving and quality control issues. However, the loss of curing water due to evaporation reduces internal curing efficiency in high w/c ratio mixes. This research evaluates a novel approach to minimizing internal curing water loss at an early age by combining internal curing with permeability-reducing admixtures (PRA) and shrinkage-reducing admixtures (SRA). Different mixtures containing binary and ternary combinations of admixtures and internal curing agents were investigated. According to the findings, admixtures such as SRA and PRA can play a vital role in maximizing the potential of internal curing in high w/c mixes. Furthermore, the ternary combination of LWA and the two admixtures has proven promising based on the observed overall improvement in NSC properties.

A novel strategy to reinforce double network hydrogels with enhanced mechanical strength and swelling ratio by nano cement hydrates

Nano-reinforcement has become a promising strategy to enhance the crosslinking microstructure and mechanical properties of hydrogels. In this study, a new type of nanomaterials from cement hydration, nano-calcium-silicate-hydrate (nano-C-S-H) gels, was for the first time to be adopted to strengthen the double network hydrogels, consisting of N-isopropylacrylamide and sodium acrylate. The experimental results indicated that 10 wt% addition of nano-C-S-H gels contributed to 40% and 157% enhancement in swelling ratio and compressive strength of N-isopropylacrylamide-co-sodium acrylate (Poly(NIPAm-SA)) hydrogels, respectively, which was attributed to the stronger chemical interactions between the nano-C-S-H gels and polymer matrix. Furthermore, 10 wt% addition of nano-C-S-H gels also improved the thermal stability of Poly(NIPAm-SA) hydrogels by 3.7%. In conclusion, the developed nano-C-S-H gels reinforced Poly(NIPAm-SA) hydrogels have great potential to be used as an efficient internal curing agent to develop high-performance concrete.

Shrinkage of high-strength engineered cementitious composite with zeolite particles as internal curing agent

The shrinkage and internal relative humidity (RH) of internally cured high-strength engineered cementitious composites (HSECCs) based on ordinary Portland cement (OPC) were experimentally investigated. Natural zeolite and calcined zeolite particles were used as internal curing agents. The effect of calcination and substitution ratio of zeolite on the shrinkage reduction efficiency and the compressive strength of the composites was evaluated. The test results showed that the development of shrinkage and internal RH of the OPC-HSECCs followed a two-stage pattern. Regarding shrinkage reduction of the OPC-HSECCs, the efficiency of the pre-wetted calcined zeolite particles was greater than that of the natural zeolite; the total shrinkage was reduced by more than 54% at 28 days and the compressive strength was similar to the control. The optimum replacement ratio of calcined zeolite was determined to be around 30%.

Effect of absorption determining methods of superabsorbent polymers in cementitious environments on the fresh properties

Autogenous shrinkage can be mitigated by the use of superabsorbent polymers (SAP) as internal curing agents. SAP are a competitive alternative to lightweight aggregates since SAP could absorb water 20–30 times by its mass in cementitious environments. There is no general agreement on determining the absorption capacity of SAP in cementitious environments. In this study, the absorbency of SAP was determined with the teabag, flow table, and point-count (ASTM C 457) methods. Two SAP with different particle sizes (D50: 215 µm and D50: 725 µm) were used in the mixtures to examine the effect of particle size on fresh properties. Also, two concrete types (slurry infiltrated fiber concrete’s matrix and ordinary mortar) to examine the usability of the methods in different rheological characteristic concretes. This study aimed to use optimal additional water without compromising workability and w/c ratio. Absorption capacities were found to be lower for the point-count method since the flow table method are not taking into account the filler effect of SAP in the mixtures. Using the absorption values obtained from the point-count method, affected slurry infiltrated fiber concrete’s fresh properties negatively. On the other hand, it has been found that this effect was limited for ordinary mortars. Results indicated that even though the point-count method could be more accurate, concrete type is also important when choosing a method to determine the absorption capacity of SAP.

Extract of Biomaterial as Admixture for Internal Curing Agent for Concrete

Extract of Biomaterial as Admixture for Internal Curing Agent for Concrete

Understanding the shrinkage behaviour of alkali-activated slag binders modified by the superabsorbent polymer

Superabsorbent polymers (SAPs) have gained attention as internal curing agents in alkali-activated slags (AAS). The absorption–desorption kinetics of SAPs in AAS pastes were monitored using X-ray computed tomography. This study examines the influence of Angular covalently crosslinked sodium polyacrylate SAPs on AAS's reaction kinetics, pore structure, and microstructure f AAS. Meanwhile, autogenous, total drying shrinkage and continuous monitoring of internal relative humidity changes were performed. The results showed that the SAPs’ desorption kinetics is crucial in influencing the efficiency to counteract the shrinkage. SAPs significantly mitigated the autogenous and total drying shrinkage up to 90% and 30%, respectively.The incorporation of the ideal content of SAPs significantly compensated for the impact of the w/b ratio AAS properties. The optimum SAPs dosage was found to be 0.6 %, which enhanced the ability to control IC water, yielding better performance in terms of shrinkage, assisting the hydration degree, and enhancing the surface quality and anti-permeability. No reaction products were detected inside the voids of SAP, and the agglomeration of SAP was observed. However, care should be taken when incorporating a high content of SAP (i.e. > 0.6 %), which can adversely affect the properties of AAS. This work confirms that IC of AAS using SAPs is a powerful mitigating strategy, particularly when traditional curing is insufficient.

Internal curing for high-performance concrete by a green composite capsule

Improving concrete eco-efficiency is a challenging and ongoing topic in response to the sustainability requirements for modern concrete infrastructure. This study proposed a novel, biobased internal curing (IC) agent material for high-performance concrete. A two-step physical method was successfully developed to turn organic alginate and inorganic fly ash into a high-value-added green composite capsule, where the internal alginate bead reserves abundant IC water and the external robust shell supplies the protection to realize steady water release. The composite capsules with a core-shell structure have a particle size of 850 ± 20 μm, shell thickness of 65 ± 10 μm and water content of 40 wt%. Moreover, the IC effect of composite capsules on cement paste was monitored by the hydration process, the setting time and microstructural observation. Further IC efficiency was quantified by autogenous shrinkage and compressive strength. The results indicate that it is feasible to use the proposed green composite capsules for internally cured high-performance concrete. The composite capsules can not only effectively decrease the autogenous shrinkage but also eliminate the negative degradation of the compressive strength of concrete due to the incorporation of IC agents. The novel IC agent represents superiorities in terms of IC efficiency and sustainability.

Effect of internal curing on early-age properties of concrete under simulative natural environment in arid regions

The potential for the use of internal curing in concrete under a natural environment remains unclear. Therefore, this research concerns understanding the effects of three internal curing agents (superabsorbent polymers (SAP), lightweight aggregate (LWA), and perforated cenospheres (PCs)) on the early-age properties of concrete under simulative natural environment in arid regions. Concrete specimens selected underwent a daily temperature cycle from −5 °C to 40 °C and a constant relative humidity of 35 % in an environment chamber prior to various macro-/micro-structural tests. Compressive strength, splitting tensile strength, autogenous shrinkage, crack resistance characteristic as well as morphology, phase composition and pore-structure were measured. Results show that only internal curing via SAP can increase 28-d compressive strength because large pores in concrete are transformed into small ones by promoting cement hydration. Furtherly, internal curing can reduce both temperature sensitivity and autogenous shrinkage of concrete and improve crack resistance. The analysis reveals that the compressive strength and early-age autogenous shrinkage of internally cured concrete are greatly affected by extra water to cement ratio ((w/c)IC), both decrease as (w/c)IC increases. Moreover, the rate of water release from internal curing agents also affects autogenous shrinkage of concrete and LWA had a higher early-age water release rate than PCs. After comparison, SAP is more suitable for the arid regions with large temperature variation and the best content of it is 0.2–0.3 % of cementitious materials.

Thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) hydrogel particles improve workability loss and autogenous shrinkage in cement paste

In this work, we show that non-superabsorbent, thermo-responsive poly(N-isopropyl acrylamide) (PNIPAM) hydrogel particles (< 250 μm) can reduce autogenous shrinkage in cement paste and improve early-age stiffening that can be caused by traditional superabsorbent polymers (SAPs). Swelling measurements in DI water and cement filtrate solution suggest that SAP-induced early-age stiffening is caused by its super-absorbency in low-ionic solutions – a behavior not exhibited by non-superabsorbent PNIPAM. Addition of PNIPAM resulted in a 29% and 60% reduction in autogenous shrinkage strain at 14 days when used alone (0.3 wt% PNIPAM) and in combination with SAP (0.15% PNIPAM, 0.15% SAP), respectively, compared to a Control with no polymer addition. Furthermore, an addition of 0.3 wt.% PNIPAM exhibited a ∼29% and ∼37% decrease in static yield stress compared to a Control and 0.3 wt% SAP-modified cement pastes, respectively. Taken together, the results provide initial evidence to suggest that the use of hydrogels as internal curing agents may not necessarily require super-absorbency to reduce autogenous shrinkage. Non-superabsorbent hydrogels, like PNIPAM, may help reduce autogenous shrinkage while alleviating the effects of SAP-induced early-age stiffening.