Internal Curing Agents Research Articles

Long-term shrinkage performance and anti-cracking technology of concrete under dry-cold environment with large temperature differences

• The basic mechanical properties of long-age concrete under dry-cold environment with large temperature differences are analyzed. • The free shrinkage of long-age concrete under dry-cold environment with large temperature differences is analyzed. • The constrained shrinkage of long-age concrete under dry-cold environment with large temperature differences is analyzed. • The microstructure of long-age concrete under dry-cold environment with large temperature differences is analyzed. Shrinkage performance and anti-cracking technology of concrete in a dry-cold environment and large daily temperature differences (-20℃∼15℃) are investigated through environmental simulation tests. According to on-field practice, after 28-day standard curing, concrete specimens are placed in the simulated environment and under five different maintenance methods, which are natural exposure (NE) as reference, membrane curing (MC), coating curing (CC), curing with expansive agent (CE), and curing with both expansive and internal curing agent (CEI). A novel nano-ceramic coating is used in CC. The mechanical properties, free shrinkage rate, restrained shrinkage rate, and porosity by mercury intrusion porosimetry (MIP) of specimens after freezing age of 0 ∼ 56-d are measured. Both compressive strength ( f cu ) and tensile strength ( f t ) of NE and CE decrease evidently with freezing age, and f cu and f t for CC, MC, and CEI scenarios are slightly affected by freezing age. Both free shrinkage and restrained shrinkage are mainly due to the temperature deformation; the drying shrinkage takes only about 21 % of the total shrinkage. The cyclic temperature differences lead to accumulation of maximum restrained shrinkage stress in concrete. Shrinkage performances are highly dependent on curing methods; the order of anti-cracking performance from the best to worst is: CC, MC, CEI, CE, NE. Adding expansion agents alone (CE) is insignificant in reducing the shrinkage, which can be compensated by furthering adding internal curing agents (CEI). The moisturizing effect of internal curing agent, membrane, and coating contribute to better microstructure, strength development, and shrinkage mitigation. The thermal insulation and the bonding effect of CC further reduce the free shrinkage and restrained stress, thus presenting the strongest resistance to shrinkage and induced cracking. The porosity and most probable pore size (MPPS) from MIP tests are consistent with results of strength and shrinkage. Overall, specimens under CC show the best overall performances under simulated environment.

Mitigating Autogenous Shrinkage of Alkali-Activated Slag Mortar by Using Porous Fine Aggregates as Internal Curing Agents

Alkali-activated slag (AAS) is beneficial for resource conservation in that it consumes little primary industrial energy, and it also performs well in terms of its mechanical properties and durability. However, its higher autogenous shrinkage compared to OPC mortars is a serious issue impeding AAS-based binder development for practical applications. This study investigated the feasibility and performance of active recycled aggregates when applied as man-made internal curing agents (MAs) for AAS mortars. They were applied as aggregate replacements for sand in this study to investigate the effects on the autogenous shrinkage, internal relative humidity (IRH), compressive strength, hydration properties and pore structure of AAS mortars. Three MAs with the sizes of 0.63–1.25 mm (MA 0.63), 1.25–2.5 mm (MA 1.25) and 2.5–4.75 mm (MA 2.5) were used. The results showed that MAs have potential as internal curing agents to mitigate the autogenous shrinkage of AAS mortars. When using saturated MAs, the autogenous shrinkage of AAS mortars was reduced by 87.68%. The addition of MAs also significantly prolonged the critical time taken for the IRH to start decreasing from 100%.

Improving the pore structure of perforated cenospheres for better internal curing performance

The pore structure of internal curing agents can significantly influence their effectiveness in reducing the autogenous shrinkage of cementitious materials with low w/b ratios. Optimization of their pore structures is meaningful, whereas it is rarely concerned. This study demonstrates that the pore structure of the perforated cenosphere can be adjusted to achieve a better internal curing performance. Increasing the etching duration can expose the own pores of cenospheres at an etching concentration of 0.7 M, gradually increasing the porosity of the perforated cenospheres. A higher etching solution concentration can significantly increase both size and number of the perforating holes. The results of the desorption properties test showed that more porous perforated cenospheres released up to about 90 % of the carried water to the surrounding environment at a higher rate, thereby achieving better effectiveness in reducing the autogenous shrinkage of low w/b cement mortars. An optimal etching condition that an etching duration of 15 min and a concentration of etching solution of 0.7 M were confirmed to prepare perforated cenospheres to almost eliminate the autogenous shrinkage of cement mortars. In addition, it is confirmed that a non-volatile acid, oxalic acid, can be used to replace hydrochloric acid to prepare the etching solution for cenospheres.

Application of Polyacrylic Hydrogel in Durability and Reduction of Environmental Impacts of Concrete through ANN.

While adding superabsorbent polymer hydrogel particles to fresh concrete admixtures, they act as internal curing agents that absorb and then release large amounts of water and reduce self-desiccation and volumetric shrinkage of cement that finally result in hardened concrete with increased durability and strength. The entrainment of microscopic air bubbles in the concrete paste can substantially improve the resistance of concrete. When the volume and distribution of entrained air are adequately managed, the microstructure is protected from the pressure produced by freezing water. This study addresses the design and application of hydrogel nanoparticles as internal curing agents in concrete, as well as new findings on crucial hydrogel–ion interactions. When mixed into concrete, hydrogel particles produce their stored water to power the curing reaction, resulting in less volumetric shrinkage and cracking and thereby prolonging the service life of concrete. The mechanical and swelling performance qualities of the hydrogel are very sensitive to multivalent cations found naturally in concrete mixes, such as aluminum and calcium. The interactions between hydrogel nanoparticles and alkaline cementitious mixes are described in this study, while emphasizing how the chemical structure and shape of the hydrogel particles regulate swelling behavior and internal curing efficiency to eliminate voids in the admixture. Moreover, in this study, an artificial neural network (ANN) was utilized to precisely and quickly analyze the test results of the compressive strength and durability of concrete. The addition of multivalent cations reduced swelling capacity and changed swelling kinetics, resulting in fast deswelling behavior and the creation of a mechanically stiff shell in certain hydrogel compositions. Notably, when hydrogel particles were added to a mixture, they reduced shrinkage while encouraged the creation of particular inorganic phases within the void area formerly held by the swelled particle.

Alginate- and sulfonate-based superabsorbent polymers for application in cementitious materials: Effects of kinetics on internal curing and other properties

Superabsorbent polymers have been widely investigated for internal curing in cementitious materials. In most cases, commercial SAPs are used and not enough information is available regarding their chemical composition. Efficient and optimal application of SAPs in cementitious materials depends on chemical composition and its effects on the properties of the material. Being able to relate and predict the behavior of SAPs and fine tune properties for specific applications are of utmost importance. In this paper, eight different innovative and “in-house” produced polymers (based on alginates and sulfonates) are studied as internal curing agents in cement pastes and compared to commercially available SAPs. The different kinetics of water sorption and desorption and its effects on mitigation of autogenous shrinkage and other properties are thoroughly discussed and linked to chemical composition of SAPs, providing recommendations on the selection of the appropriate SAPs for different application in cementitious materials.

Hydrophobic hydrogels as internal curing agent for concrete: The double benefit of super high water content and excellent anti-ion permeability

Owing to their high water content, conventional superabsorbent polymer (SAP) hydrogels can serve as internal curing agents for concrete fabrication. However, the hydrophilic network in such hydrogels permits ion diffusion, which induces severe steel corrosion inside concrete in the marine environment. Herein, we introduce a brand-new hydrogel, termed “hydrophobic hydrogels”, for concrete curing. On one hand, these hydrogels possess super high water content (up to 99.6 wt%), which is even higher than that in normal SAP hydrogels; on the other hand, the anhydrous inhomogeneous hydrophobic structures can significantly retard or stop the ion permeation, which is significantly superior to SAP hydrogels. With ion diffusion measurement, the hydrophobic hydrogels achieve much better ion resistance than SAP hydrogels, with 2–5 orders' decrease in ion permeation rate. Among diverse hydrophobic hydrogels, the polymer's hydrophobicity and glass transition directly determine the permeation performance. Hydrogels with a more hydrophobic network and higher polymer Tg possess better anti-ion diffusion properties. At the optimal state, the poly(phenyl acrylate) hydrophobic hydrogels can completely stop the permeation process. Owing to the double benefit, the hydrophobic hydrogel cured concretes demonstrate a notable decrease in ion permeation compared to SAP hydrogel cured concrete, with only 1/20 of ion permeation to that in SAP groups with an electric flux test upon coated on the surface layers. Owing to the double benefit from super high water content and excellent anti-ion permeability, these hydrophobic hydrogels may serve as ideal candidates as concrete curing agents in the future.

Upgrading sodium montmorillonite into a reactive internal curing agent for sustainable cement composites through non-ionic functionalization

The role of non-ionic functionalization in modifying the physical and chemical properties of clay minerals and their potential as internal curing agents in cement composites have been remaining unclear. This work elucidates comprehensive insights into the functionalization of sodium montmorillonites (sMTs) with two non-ionic surfactants, t-octyl phenoxy poly ethoxyethanol (TX100) and polyethylene glycol ether (PEG10), and their influences on sMT properties. The results indicate that both TX100 and PEG10 are effectively intercalated into sMT resulting in increased interlayer spacing and hygroscopic swelling behavior. With the presence of functionalization, the water uptake capacity, ion exchange capacity, and dispersion of the sMT in both water and simulated cement pore solution are improved. With raised Al and Si dissolution, a significant improvement in pozzolanic reactivity of sMT is observed. Insights reported here pave a path for leveraging non-ionic functionalized sMT as a potential internal curing agent for cement hydration and concrete performance enhancement.

Effect of abaca natural fiber on the setting behavior and autogenous shrinkage of cement composite

In this study, the effects of abaca fibers on the initial hydration and autogenous shrinkage characteristics of cement were investigated with the aim of using natural abaca fibers as construction materials. Abaca fiber content was chosen as the primary experimental variable and was varied from 0 to 0.25, 0.5, 1, and 2% of the weight of cement for testing. To identify the influence of the fibers on the hydration reaction of cement, the heat of hydration, ultrasonic pulse velocity, and setting time were measured. The internal curing effect of abaca fibers was evaluated using thermogravimetry and microstructure analysis by conducting compressive strength and autogenous shrinkage tests. The results indicate that abaca fibers can be used as internal curing agents owing to their high water absorption rate, which results from the cross-sectional characteristics of their hollow bundle-type tubular structure. Abaca fibers are found to be an effective alternative that can mitigate the risk of cracking by reducing the autogenous shrinkage of high-performance cement concrete products.

The Numerical Analysis of Replenishment of Hydrogel Void Space Concrete Using Hydrogels Containing Nano-Silica Particles through ELM-ANFIS.

Currently, Nano-materials are gaining popularity in the building industry due to their high performance in terms of sustainability and smart functionality. In order to reduce cement production and CO2 emissions, nano-silica (NS) has been frequently utilized as a cement alternative and concrete addition. The influence of Nano-silica-containing hydrogels on the mechanical strength, electrical resistivity, and autogenous shrinkage of cement pastes was investigated. The goal of this study was to identify the main structure–property relationships of water-swollen polymer hydrogel particles used as internal curing agents in cementitious admixtures, as well as to report a unique synthesis process to combine pozzolanic materials with hydrogel particles and determine the replenishment of hydrogel void space. Experiments were designed to measure the absorption capacity and kinetics of hydrogel particles immersed in pure water and cementitious pore solution, as well as to precisely analyze the data derived from the tests using hybridized soft computing models such as Extreme learning machine (ELM) and Adaptive neuro-fuzzy inference system (ANFIS). The models were developed, and the findings were measured using regression indices (RMSE and R2). The findings indicated that combining nano-silica with polymeric hydrogel particles creates a favorable environment for the pozzolanic reaction to occur, and that nano-silica assists in the refilling of hydrogel void space with hydrated cement phases.

Improving the Self-Healing of Cementitious Materials with a Hydrogel System.

Despite cement’s superior performance and inexpensive cost compared to other industrial materials, crack development remains a persistent problem in concrete. Given the comparatively low tensile strength, when cracks emerge, a pathway is created for gas and water to enter the cementitious matrix, resulting in steel reinforcement corrosion which compromises the durability of concrete. Superabsorbent hydrogels have been developed as a novel material for enhancing the characteristics of cementitious materials in which they have been demonstrated to decrease autogenous shrinkage and encourage self-healing. This study will detail the design and application of polyelectrolyte hydrogel particles as internal curing agents in concrete and provide new findings on relevant hydrogel–ion interactions. When hydrogel particles are mixed into concrete, they generate their stored water to fuel the curing reaction that results in less cracking and shrinkage, thereby prolonging the service life of the concrete. The interaction of hydrogels with cementitious materials is addressed in this study; the effect of hydrogels on the characteristics and self-healing of cementitious materials was also studied. Incorporating hydrogel particles into cement decreased mixture shrinkage while increasing the production of particular inorganic phases within the vacuum region formerly supplied by the swollen particle. In addition, considering the control paste, cement pastes containing hydrogels exhibited less autogenous shrinkage. The influence of hydrogels on autogenous shrinkage was found to be chemically dependent; the hydrogel with a delayed desorption rate displayed significantly low shrinkage in cement paste.

Delayed Absorption Superabsorbent Polymer for Strength Development in Concrete.

Superabsorbent polymers (SAPs) are used as internal curing agents in cementitious materials, which reduce autogenous shrinkage in concrete as they have a low water-to-cement ratios and improve the freeze–thaw resistance. However, the compressive strength of concrete may also be reduced due to additional voids in the hydrated cement matrix. In this study, we fabricated a delayed absorption type of SAP (I-SAP) composed of cross-linked modified acrylate and studied its absorption characteristics and effect on compressive strength after 28 days. Furthermore, the effect of curing conditions on the strength of concrete and hydrated cement paste with SAP were investigated. The absorption capacity of I-SAP in the synthetic pore solution and deionised water was examined and compared with that of a conventional SAP, and the former was absorbed more by I-SAP. The results revealed that the compressive strength of concrete increased with the addition of I-SAP, particularly with the curing condition of 60% RH. Although the compressive strength of hydrated cement paste with I-SAP reduced in water or sealed curing conditions, no loss of strength in the paste cured at 60% RH was seen. The cement matrix densification due to hydration of belite around the SAP surface is the main mechanism for strength development in concrete cured at sealed and 60% RH. However, the voids formed by SAP control the compressive strength of hydrated paste.

A Review on the Use of Self-Curing Agents and Its Mechanism in High-Performance Cementitious Materials

Self-cured concrete is a type of cement-based material that has the unique ability to mitigate the loss rate of water and increase the capacity of concrete to retain water compared to conventional concrete. The technique allows a water-filled internal curing agent to be added to the concrete mixture and then slowly releases water during the hydration process. Many researchers have studied the composition of self-curing concrete using different materials such as artificial lightweight aggregate (LWA), porous superfine powders, superabsorbent polymers (SAP), polyethylene glycol (PEG), natural fibers, and artificial normal-weight aggregate (ANWA) as curing agents. Likewise, physical, mechanical, and microstructure properties, including the mechanisms of curing agents toward self-curing cement-based, were discussed. It was suggested that adopting self-curing agents in concrete has a beneficial effect on hydration, improving the mechanical properties, durability, cracking susceptibility behavior, and mitigating autogenous and drying shrinkage. The interfacial transition zone (ITZ) between the curing agent and the cement paste matrix also improved, and the permeability is reduced.

Effect of bio-based internal curing agent on the performance of high-performance mortar

This paper examines the feasibility of using corncob particles as an internal curing agent in high-performance mortar. Due to the adverse effects of corncob leachate on cement hydration, the corncob particles were first treated by successive soaking in tap water. The effects of the corncob particle content, size, and state (pre-saturated or dry) on the internal relative humidity, autogenous shrinkage, mechanical properties, heat evolution, hydration products, and microstructure of high-performance mortar were investigated. The results indicated that the leachate of treated corncob particles resulted in a reduced setting time, more hydration products, and improved mechanical properties compared to the leachate of untreated corncob particles. The treatment was effective, and the mortar exhibited a similar performance as the reference mortar. The incorporation of corncob particles effectively reduced the drop rate of relative humidity and autogenous shrinkage. This result was attributed to the internal curing of the corncob particles, which delayed self-desiccation and promoted cement hydration. Increases in the heat release and the amount of hydration products confirmed the internal curing of the corncob particles. The corncob particles improved cement hydration, but the mechanical properties were adversely affected due to the weakness of the corncob particles and the poor interface between them and the cement matrix. The results suggest that small and pre-saturated corncob particles provided the best internal curing performance.

Studies on the influence of alginate as a natural polymer in mechanical and long-lasting properties of concrete – A review

In the present, as the primary spotlight on economic development increases, green concrete material takes on a significant job in a realistic turn of events. The usage of durable concrete determines a structure's capacity to maintain itself. A concerted attempt was made to achieve long-term sustainability. Those endeavours make the green concrete development 'green', less energy, and fewer fossil fuel by-products. Marine brown seaweed is a natural biopolymer available along the coastal regions that give copious benefits like soil stabilization, heat capacity characteristics and carbon dioxide fixation. Alginate is a natural hydrogel detached from the cell walls of marine brown algae. It improves the toughness of material and is also apply in unfired clay bricks, internal curing agents, and viscosity-enhancing admixtures. This paper aims to review the application ofalginate based seaweed as natural polymer in properties of concrete.

Internal curing efficiency and key properties of UHPC influenced by dry or prewetted calcined bauxite aggregate with different particle size

A strong and porous aggregate (calcined bauxite, CB) has been applied as novel internal curing (IC) agent in UHPC to counteract its high autogenous shrinkage. However, in view of intelligently UHPC mixture design to acquire satisfactory workability, mechanical properties, and low-shrinkage UHPC, the influences of CB particle size and IC water incorporation methods are not well explored yet, and thereby are investigated in this study. UHPCs with different particle sizes (1 ∼ 3 mm, 3 ∼ 5 mm, and 5 ∼ 8 mm) of CB and methods of prewetting CB or using dry CB with adding IC water during mixing were investigated, together with preparing a reference UHPC (no CB). Multiple microstructural characterization techniques were used to explore the underlying mechanisms. Results show that the UHPCs with any condition of CB aggregate all obtained promoted mechanical properties and significantly reduced autogenous shrinkage compared to the reference UHPC. The large CB led to the highest compressive strength increment while the small and medium CB resulted in similar increments; more shrinkage reduction (higher IC efficiency) was achieved with the medium or small CB (above 70% reduction) than with large CB (58% reduction). The prewetting practice resulted in slightly more strength increment than using dry CB with adding IC water during mixing, and these two practices reached similar IC efficiency. Microstructural analysis with TG test and BSE observation confirmed the promoted hydration in the UHPCs caused by the IC effect of CB aggregate; reduced total porosity was observed in these UHPCs with CB by MIP test.

Environmentally friendly utilization of coal gangue as aggregates for shotcrete used in the construction of coal mine tunnel

Coal gangue is one of the largest discharged industrial solid wastes, which is generated in the processes of coal mining and washing. To accelerate the in-situ utilization of coal gangue, this paper explored coal gangue aggregates (CGA) as the single aggregate source to prepare shotcrete used for coal mine tunnel underground in local. The effects of CGA rates and water/binder ratio (w/b) on CGA shotcrete were experimentally studied by means of the compressive strength, chloride permeability determined by electric flux method, pore structure measured by Nuclear magnetic resonance (NMR), and elastic modulus of interface transition zone (ITZ) investigated by nanoindentation. Besides, the environmental effects were discussed based on the material sustainability indicators. It was found that CGA rate played important roles in affecting the compressive strength and durability of CGA shotcrete. By increasing CGA rate from 62% to 71%, the 28d compressive strength of CGA shotcrete firstly increased and subsequently decreased independent with w/b; and the electric flux can be greatly reduced. The total porosity of CGA shotcrete with CGA rate depends on w/b. When w/b was high like 0.43 or 0.50, with the increase of CGA rate, the total porosity of CGA shotcrete decreased continuously. Due to the porous structure of CGA, it can adjust the water distribution around the aggregates and served as internal curing agents, contributing to stronger elastic modulus of ITZ. By incorporating 71% CGA, the total energy consumption and the CO2 emission of CGA shotcrete have been reduced by 24–32%, and 12–24%, respectively. This paper confirmed the feasibility of using CGA as the single aggregates source for shotcrete, which make significance to the utilization of CGA in a large scale.

Design and application of UHPC with high abrasion resistance

This study presents the design and application of concrete with enhanced abrasion resistance and volume stability. Specifically, Ultra-high performance concrete (UHPC) is selected as a promising matrix for abrasion resistance application due to the introduction of silica fume and steel fiber. Then, locally available manufactured sand (MS) has been added to the matrix to further improve the abrasion resistance. To expand the field application of UHPC based abrasion resistance material, the volume stability has been enhanced via the employment of internal curing agent (ICA) and expansive agent (EA). The effect of factors, i.e., the needle-like content in MS, the steel fiber dosage, the single and synergistic effect of the addition of ICA and EA, has been studied systematically. The results confirmed the positive effect attributed by the introduction of high needle-like content MS and steel fiber in the enhancement of anti-abrasion property, while highlighted the advance caused by the combined use of ICA and EA in improving the volume stability. After that, via a step-by-step design methodology, an optimized proportion of anti-abrasion UHPC can be determined. Moreover, the field application of the developed anti-abrasion UHPC has also been comparatively studied.

Potential usage of porous autoclaved aerated concrete waste as eco-friendly internal curing agent for shrinkage compensation

Autoclaved aerated concrete waste (AACW) is an inorganic porous construction and demolition waste, which is possible to be environmentally used as an internal curing agent, due to its water absorption and release characteristics. In present work, fine aggregate (sand) was replaced by AACW aggregate with the same volume for internal curing purpose. The potential curing effect of AACW was also compared with a classical internal curing agent, i.e. expanded perlite (EPA), under the same particle size condition. Results indicate that the compressive strength of AACW groups after 28-day sealing curing is basically the same as that of the control group. Compared with EPA, internal curing with AACW can better improve the internal relative humidity, reduce the autogenous shrinkage, and delay the cracking time of cement mortar. At the same time, AACW effectively refines the pore structure and improves the micro-hardness of the interfacial transition zone (ITZ) through internal curing, and enhances the resistance to chloride penetration.

Feasibility of Bentonite as an Internal Curing Agent in Concrete

Background: There is a requirement for internal curing, especially in areas where water is scarce and where it is difficult to cure concrete due to inaccessibility of the site. About five times higher water is consumed in curing than the water used in making concrete. Furthermore, the quality of water that is to be used for these activities is required to be of a certain standard. If the requirement of water can be reduced, it becomes both economically and ecologically viable. Objective: The present research is carried out to determine the technical and economic feasibility of bentonite as an internal curing agent with properties of concrete to be used in the field. Methods: This paper compares the compressive and flexural strength parameters for standard and bentonite infused concrete and whether this can be considered as a suitable addition in concrete. The flexural strength is measured using four-point test. Both the tests are carried out in accordance with IS codes. Results: There is an increase in compressive strength for both intermittent and air curing of internally cured concrete in comparison to control concrete. Furthermore, air curing of internally cured concrete is comparable to intermittent curing of control concrete. Also, the compressive strength of intermittent curing concrete with bentonite is comparable with the strength obtained by pond curing of control concrete. Conclusion: The results indicate that bentonite can be considered as a viable addition to concrete, especially in cases of air curing. The use of bentonite is thus recommended for air curing and intermittent curing conditions.

Experimental Investigation of Light Weight Aggregate with Internal Curing Agent by Using Fly ash Aggregate

The point of this research was to research the impact of a high volume of rooftop tile squander coarse total as an inside relieving specialist on compressive strength in the paste of fly-ash concrete. Interior relieving with squander total expanded the compressive strength of fly-ash concrete and diminished modulus of versatility. Squander total can be utilized as an inside repository to build the compressive strength and demonstrate cement design with high volume substitution of class-fly ash.