Expansive Agent Research Articles

Deformation and Cracking Resistance of MgO-Incorporated Cementitious Material: A Review.

In China, MgO-based expansive agent (MEA) has been used for concrete shrinkage compensation and cracking control for over 40 years. The expansive behavior of MEA in cementitious materials could be manipulated to some extent by adjusting the calcination process of MEA and influenced by the restraint condition of the matrix. It is key to investigate the factors related to deformation and cracking resistance so that the desired performance of MEA in certain concrete structures could be achieved. This paper reviews the influence of key parameters such as hydration reactivity, dosage, and calcination conditions of MEA, the water-to-binder ratio, supplementary cementitious material, aggregates, and curing conditions on the deformation and cracking resistivity of cement paste, mortar, and concrete with an MEA addition. The numerical simulation methods and deformation prediction models are then summarized and analyzed for more reasonable estimations.

An Investigation into the Effects of Oil-Well Cement Expansion Agent on the Integrity of Cement Sheath

Generally, the so-called expansion agent is very effective in eliminating all the micro-annuli that exist between the casing and the cement sheath or between the cement sheath and the formation. However, this approach can detrimentally affect the sealing ability of cement sheath if the expansion agent is used in an unreasonable way. For these reasons, in the present work, numerical simulations have been conducted to analyze the effect of elasticity modulus of cement sheath, the elasticity modulus of formation, the expansion rate of cement, the geo-stress on the micro-annulus caused by cement expansion, and the cement sheath expansion on the integrity of cement sheath and formation. The micro-annulus between the casing and the cement sheath has been found to decrease according to the ratio between the elasticity modulus of formation and the elasticity modulus of cement sheath. A positive correlation has been observed between the micro-annulus and the cement expansion ratio. The micro-annulus decreases as the geo-stress increases, but the effect of the geo-stress on the micro-annulus is much smaller. In conclusion, the expansion agent is suitable for the formation in which the elasticity modulus is higher than the cement sheath.

Particle-size distribution of alumina slag after grinding

The paper considers the issues of energy consumption and effectiveness of using aluminous slag as an expansion agent compared to Portland cement. Aluminous slag is a difficult material to grind, but its use as an additive is in demand for building materials. The following research methods were used: grinding of materials, sieve analysis, electron microscopy. According to the results of studies, it was found that the use of aluminous slag as an expansion agent is effective compared to Portland cement.

Autogenous healing of hollow natural fiber (HNF)-reinforced reactive magnesium cement (RMC)

This work investigated the autogenous healing of interface bond between hollow natural fiber (HNF) (e.g., sisal fiber) and reactive magnesium cement (RMC). Preloading -reloading test was conducted to single fiber embedded specimens, the results suggested that the interface bond can be improved by over 300% after wetting-air cycles conditioning, and hot water conditioning demonstrated greater healing efficiency compared to room temperature conditioning. Based on SEM-EDS characterization, this prominent restoration of interface bond is due to: 1) further hydration and carbonation of RMC, which partially fills the microcracks between fiber and matrix; 2) the migration and precipitation of expansive agents in lumens, which improves the contact between sisal fiber and matrix. Furthermore, the interface bond healing resulted in a significant recovery of the fiber-bridging strength of sisal fiber-reinforced RMC, the fiber-bridging strength doubled after healing compared with that of preloading.

Studies on Lightweight Geopolymer Concrete

The studies on Lightweight Geopolymer concrete (LGC) are leading-edge in the development of sustainable and eco-friendly concrete. Attempts were being made to develop LGC by various methods of production. This paper reviews about previously published research work on lightweight geopolymer concrete and the observations to the material binders - an alternate to the Ordinary Portland Cement (OPC) by the utilization of industrial by-products, alkaline activator solution, foaming agents, chemical expansive agents, lightweight aggregate, production methods, and their physical and mechanical properties. The main focus is to investigate pore size formation, density, compressive strength and curing conditions. From the review it is found that the stabilization of foam and the control of efflorescence are the two challenging problems faced by the industry for the mass production of lightweight geopolymer foam concrete. Furthermore, topics for future work in this field were suggested.

Self-healing behavior of strain-hardening cementitious composites with MgO-type expansive agent after drop weight impact loading

Strain-hardening cementitious composites (SHCC) are usually subjected to a variety of dynamic loads during service period. The self-healing behavior of SHCC after damage of static loading have already been studied in detail, however, the corresponding investigation regarding the influence of dynamic loading is limited. In this paper, drop weight impact tests were used to introduce cracks into SHCC samples incorporated with MgO-type expansive agent (MEA), followed by different exposure conditions, including water, seawater, saturated Ca(OH)2 solution and 3 % NaCl solution. The self-healing effect of SHCC was evaluated by crack width, capillary water absorption and the recovery of impact resistance. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were performed to distinguish reaction products of self-healing, revealing the self-healing mechanisms. The results show that cracks with small size of SHCC incorporated with MEA can be closed under these four exposure conditions, and the crack widths <10 μm and 60 μm are completely closed after 7 days and 60 days, respectively. The normalized water absorption also shows cracked SHCC after healing in seawater have a better self-healing compared to the other three conditions, and the impact resistance of the specimens with age of 7 d after 120 d of healing in seawater is improved by 20.1 %. In addition, the microscopic analysis of SEM, XRD and TGA shows that the main reaction products of self-healing in seawater and 3 % NaCl solution are portlandite, calcite and brucite.

Improving the carbonation resistance of alkali-activated slag mortars with different additives: experimental evaluations

The poor carbonation resistance is one of the critical reasons that restrict the application of alkali-activated slag (AAS). Different contents of calcined Mg-Al layered double hydrotalcite (CLDH), Portland cement clinker (PCL) and MgO expansive agent (MEA) were adopted to improve the carbonation resistance of alkali-activated slag mortars (AASM). In addition to the workability, the effect of additives on the carbonation behavior was systematically investigated by means of the phenolphthalein test, scanning electron microscopy (SEM), X-ray diffraction (XRD), and N2 absorption. Results showed that all three additives could improve the carbonation resistance of AASM. In terms of carbonation resistance, the optimum contents of CLDH, PCL, and MEA were 6.0%, 2.0% and 4.0%, respectively. Microstructure analysis revealed that the improvements in the carbonation resistance were mainly attributed to the structure reconstruction of CLDH, hydration products promoted by PCL, and compensation shrinkage of MEA, respectively.

Effect of additional water or superplasticizer on key characteristics of cement paste made with superabsorbent polymer and other shrinkage mitigating materials

The use of superabsorbent polymer (SAP) coupled with expansive agent (EA) or shrinkage-reducing admixture (SRA) can effectively reduce shrinkage of cement-based materials. However, SAP particles at high contents can adversely affect rheological and mechanical properties. Securing proper workability can be accomplished by additional water or adjusting the superplasticizer (SP) demand. There is an uncertainty about the efficiency of these approaches to workability compensation. This study evaluates the effect of additional water or SP on key properties of cement paste made with SAP and relatively high content of EA or SRA. Macro and micro mechanisms underlying the effect of combined shrinkage mitigating strategies on the performance of cement paste made with 0.4 water-cementitious materials ratio are investigated. Results indicate higher efficiency of increasing SP demand by 0.6% versus the addition of water by 30 g per gram of SAP. Up to 80% higher compressive strength is obtained for the mixtures made with additional SP, which is attributed to up to 33% reduction in capillary porosity and smaller pore-size distribution of the hydrated cement paste. In the presence of high EA content, the use of additional SP prevents excessive initial expansion in the paste with additional water.

Mitigating shrinkage in ultra-high performance concrete using MgO expansion agents with different activity levels

To mitigate the shrinkage properties of ultra-high performance concrete (UHPC), MgO expansion agents (MEAs) with different activity levels (R-MEA, M-MEA, and S-MEA) were prepared and incorporated into UHPC. The effect of MEA activity on the mechanical properties and volumetric stability of UHPC were evaluated by using hydration heat tests, XRD-Rietveld quantitative analysis, MIP, X-CT and SEM. The results showed that MEA addition reduces the mechanical properties of UHPC, especially at high activity levels. However, it is beneficial for compensating early shrinkage. By combining MIP and X-CT analyses, it was found that MEA effectively increases the porosity of UHPC, with R-MEA (with the strongest activity) increasing it most. The w/b ratio had a greater effect on MEA hydration than the activity level. At lower w/b ratios, R-MEA reduced autogenous shrinkage even less effectively than M-MEA. Considering both the mechanical properties and shrinkage-reducing effect, it is recommended to prepare shrinkage-reducing UHPC with a w/b ratio of 0.18 and moderately reactive M-MEA.

Design and preparation of high-performance polymer mortars based on performance prediction model

This article had presented a systematic and adjustable method to forecast the performance of certain type of polymer mortars, most of all, using the performance prediction model to accurately control the dosages of water reducing agent (D WR ), cellulose (D C ), polypropylene fiber (D F ), expansion agent (D EA ), redispersible emulsion powder (D REP ), and cement content (C C ), according to the changes of properties of polymer mortars. The article had given a full verification supported by a series of orthogonal experiment results to demonstrate the effectiveness and the feedback loop between raw materials and properties of polymer mortars, which had revealed a big practical value and convenience for rapid construction in the job sites, especially for researchers and engineers in the field. Its effort to avoid, or at least control the damage of polymer powders to compressive strength of cement mortars. The mix proportion of high-performance polymer mortars (HPMs) was determined as follows, considering the working and mechanical properties: D WR was 0.85 g, D C was 1.05 g, D F was 1.15 g, C C was 42%, D EA was 10 g, and D REP was 20 g. Successfully created HPMs with pumping resistance of just 61.6N, compressive strength of 68.5MPa at 28d.

Effects of CNT and MgO–Type Expansive Agent on the Cracking Resistance of Face-Slab Concrete of CFRD

Effects of CNT and MgO–Type Expansive Agent on the Cracking Resistance of Face-Slab Concrete of CFRD

Rheological, deformation behaviors and mechanical changes of MgO-containing concretes with different strength

MgO content is of importance to the compensation feasibility and soundness of concrete, especially for concrete with different strength grades. The rheological, deformation behavior, and mechanical changes of MgO expansive agent (MEA) (5–8 wt%) in different strength grades of concrete were revealed. Results show that MEA replacement of cement makes the yield stress and plastic viscosity increasing because of the high specific surface and agglomeration of MEA. Although same quantity of Mg(OH)2 is generated, concretes with different strength grades display different expansion behaviors because of their different pore structures and Mg(OH)2 morphology. Mg(OH)2 that growing around MgO particles presents a colloidal morphology, while Mg(OH)2 that growing in the surrounding pores presents a hexagonal flake-like morphology. The restrained deformation of Grade 40 concrete with 6 wt% MEA after curing in water for 14 d increases to the maximum expansion, reaching 237 × 10−6.6 wt% MEA replacement does not affect the compressive strength and splitting tensile strength of concrete with different strength grades. However, 7–8 wt% MEA replacement reduces the splitting tensile strength of Grade 40 concrete, and the negative impact is particularly pronounced after air curing.

Multiphysics simulation for concrete early-age hydration behavior with mesoscopic modelling

The early-age hydration behavior of concrete is of great significance for structural construction and service performance. Hydration is a complex multiphysics process coupling the field of chemical reaction, humidity transport, heat conductivity, and mechanical response. The random distribution of different phases in the material has a marked impact on hydration, and the material’s mesoscopic feature is also important for the accurate prediction of concrete hydration behavior. Combining the material mesoscopic feature and multiphysics hydration mechanism, a comprehensive theoretical framework is proposed with detailed material modelling and physics coupling relationship in this paper. Besides the overall simulation procedure, the study on model modification methods for different curing environments and different concrete materials, especially the influence of expansion additives, is also conducted. Based on the application of concrete material and specified expansion agent in engineering, experiments are carried out to investigate the hydration process and mechanical shrinkage of concrete. The results are used for parameter regression and model validation. With the model's advantages in describing multiphysics influence and the mesoscopic features, the detailed time-dependent hydration process and spatial distribution of related physics can be simulated precisely and conveniently. At last, the influences of environmental states and mixing parameters on concrete hydration behavior are investigated, and the control of curing humidity and aggregate details is found necessary.

Study on The Adhesion Properties of Light-ransmitting Concrete Based on Different Matrix Materials

Light-transmitting concrete prepared by the combination of light-transmitting materials and concrete matrix is a new building material with functions of energy saving and consumption reduction. In this paper, the current research status of scholars in this field at home and abroad is integrated and explored, so as to carry out the analysis of the interfacial bonding performance between the light-transmitting material and the concrete matrix of light-transmitting concrete. This paper selects acrylic as the light-transmitting material, silicate cement mortar, alkali magnesium sulfate cement mortar, ordinary mortar with cork particles, ordinary mortar with expansion agents, ordinary mortar with basalt fibers, and self-compacting cement mortar as the matrix materials, and tests the interfacial bonding performance of different substrates of light-transmitting concrete made by them. Through the interfacial bonding performance test and compressive strength test, the results of the study showed that the interfacial bonding between the concrete matrix and acrylic with the addition of basalt fibers was superior.

Influences of MgO and PVA Fiber on the Abrasion and Cracking Resistance, Pore Structure and Fractal Features of Hydraulic Concrete

Abrasion resistance and cracking resistance are two important properties determining the normal operation and reliability of hydropower projects that are subjected to erosion and abrasive action. In this study, polyvinyl alcohol (abbreviated as PVA) fiber and magnesium oxide expansive agents (abbreviated as MgO) were used together to solve the problems of cracking and abrasive damage. The effects of PVA fiber and MgO on the mechanical property, abrasion and cracking resistance, pore structures and fractal features of high-strength hydraulic concrete were investigated. The main results are: (1) The incorporation of 4–8% Type I MgO reduced the compressive strength, splitting tensile strength and the abrasion resistance by about 5–12% at 3, 28 and 180 days. Adding 1.2–2.4 kg/m3 PVA fibers raised the splitting tensile strength of concrete by about 8.5–15.7% and slightly enhanced the compressive strength and abrasion resistance of concrete. (2) The incorporation of 4–8% Type I MgO prolongs the initial cracking time of concrete rings under drying by about 6.5–11.4 h, increased the cracking tensile stress by about 6–11% and lowered the cracking temperature by 2.3–4.5 °C during the cooling down stage. Adding 1.2–2.4 kg/m3 PVA fibers was more efficient than adding 4–8% MgO in enhancing the cracking resistance to drying and temperature decline. (3) Although adding 4% MgO and 1.2–2.4 kg/m3 PVA fibers together could not enhance the compressive strength and abrasion resistance, it could clearly prolong the cracking time, noticeably increase the tensile stress and greatly lower the racking temperature; that is, it efficiently improved the cracking resistance to drying and thermal shrinkage compared with the addition of MgO or PVA fiber alone. The utilization of a high dosage of Type I MgO of less than 8% and PVA fiber of no more than 2.4 kg/m3 together is a practical technique to enhance the cracking resistance of hydraulic mass concretes, which are easy to crack. (4) The inclusion of MgO refined the pores, whereas the PVA fiber incorporation marginally coarsened the pores. The compressive strength and the abrasion resistance of hydraulic concretes incorporated with MgO and/or PVA fiber are not correlated with the pore structure parameters and the pore surface fractal dimensions.

Hydration and Expansion Characteristics of MgO Expansive Agent in Mass Concrete.

Based on the underground reinforced concrete wall of subway stations (Hangzhou, China), this paper studied the influence of a MgO expansive agent (MEA) on deformation and mechanical properties of a reinforced concrete wall. The results show that the effect of the MEA with different activities to compensate for the shrinkage of reinforced concrete walls is different. For MEA-R (60 s), because the activity is too high, its hydration rate is too fast, and many expansions occur at the plastic state of the concrete, which cannot effectively compensate for the shrinkage of concrete. For MEA-S (220 s), due to its low activity, the early hydration rate is so slow that it cannot compensate for the shrinkage, but it compensates well at the later stage due to the continuous hydration expansion of MEA. For MEA-M (140 s), the shrinkage of concrete is well compensated for the shrinkage at the early, middle and late stages due to its moderate activity. After using MEA to partially replace fly ash and mineral powder, the compressive strength of concrete was lower at the early stage (0-28 days). However, in the later stage, the porosity of concrete decreased rapidly, and the compressive strength of concrete would also be significantly improved. Therefore, choosing a suitably active MEA can compensate for the shrinkage of mass concrete without reducing its strength.

Influence of different additives on the creep property of oil well cement

As the exploitation of oil and gas field becomes more difficulty nowadays, severe casing deformation may occur if anti-extrusion strength of casing decreases to a certain degree and this brings large economic loss and severe safety problems. As an annular sheath between casing and formation, creep of oil well cement paste is one of the most important factors in deciding abnormal casing deformation and wellbore integrity. To figure out the mechanism on how to reduce the creep value of oil well cement paste, effect of different additives, e.g., retarder, glass fibre reinforcement and CSA expansive agent on the creep value of oil well cement are investigated in this study. It can be found out that retarder plays a negative role in reducing the creep deformation and creep value of cement with 1, 2, 3% retarder is 2.39%, 7.85%, and 15.02% higher than that without retarder at 12 h. Results from heat flow indicates that retarder may play an important role in prolonging the early induction period of hydration and reducing the hydration rate in the middle and later stages. On the contrary, Glass fibre shows a positive effect in reducing the creep value of oil well cement paste and creep value reaches with 0.2%, 0.4%, 0.6%, and 0.8% is 1.27%, 6.61%, 9.82%, and 12.60% lower than that without fibre addition at 72 h. This is because high porosity between and around fibers based on a microstructure observation may lead to a more continuous and uniform stress field between cement paste, and consequently reduce the creep value of cement paste. It can also be found out that CSA cement is considerably effective in limiting creep deformation of oil well cement paste at early ages. There is also an acceleration effect on the heat flow of oil well cement in both induction and acceleration periods and the corresponding maximum heat flow is 7.3%, 9.0%, and 11.2% higher than the reference cement with no CSA addition. The results obtained in this study are aimed to provide theoretical basis for the wellbore integrity and improvement of oil and gas recovery.

Investigating the hydration characteristics of a new composite cementitious binder containing of slag and calcite

The influence of the filler content, filler fineness and water to powder ratio (W/P) on hydration kinetics and microstructure behaviour of a new clinker-free material made of calcium hydroxide, blast furnace slag (BFS), calcite and expansive agent are explored in this study. The hydration characteristics of the proposed material were investigated by multiple experimental programmes including X-ray diffraction (XRD), TG-differential thermal analysis (DTA), selective dissolution measurement and mercury intrusion porosimetry (MIP). The experimental results revealed that slag reaction degree is enhanced by increasing the filler content and fineness of the filler in high W/P ratio. However, the filler fineness does not show significant improvement in the hydration degree of slag with low W/P ratio in later curing period due to the reduced amount of available water for the hydration reaction. Another interesting finding of this study is that the hemicarboaluminate which is thermodynamically unstable than monocarboaluminate, stably formed even at the later age of hydration reaction in the presence of calcium carbonate. The amended thermodynamic model also well agreed with the tendency of the experimental results in terms of hydration products and porosity of the hardened matrix as a function of curing period.

Development of Cement-Based Grouting Material for Reinforcing Narrow Coal Pillars and Engineering Applications

The problem needs to be solved about stability control of small coal pillars along goaf in the coal mining process. In this paper, the effects of water reducer, accelerator and expansion agent on the fluidity, setting time, expansion ratio and stone body strength of grouting materials were analyzed through orthogonal experiments, and the optimal ratio of grouting materials was obtained, and it is applied to the engineering site to obtain the reinforcement effect of the coal pillar grouting material on the coal pillar. The results of the study show that: When the dosage of the accelerating agent is 4%, the amount of water-reducer is 0.3%, and the amount of the expansive agent is 6%, the comprehensive performance of the grouting material is the best. After using the new coal pillar grouting material to strengthen the coal pillars, 30 days of monitoring were conducted to determine the deformation of the surrounding rock of the roadway. The shallow separation layer of the surrounding rock of the roadway was about 39.6~52.5 mm, and the accumulated separation layer of the deep rock was 28.5~29.5 mm, which were kept within the safe control range. The coal pillar grouting material can well fill the surrounding rock fissures and coupling and cement the broken rock mass, improve the bearing capacity of the narrow coal pillar, and enhance the overall stability of the surrounding rock of the roadway. The research results have important reference significance for similar coal pillar grouting.

Restrained cracking failure behavior of concrete containing MgO compound expansive agent under adiabatic condition at early age

The influence of MgO compound expansive agent (MCEA) on the early-age cracking failure behavior of concrete considering the influence of temperature, thermal strain, autogenous strain, and creep under the adiabatic-temperature curing mode and uniaxial restrained condition was investigated. The early-age autogenous shrinkage was effectively compensated with the addition of MCEA, and autogenous strain exhibited expansion when the dosage of MCEA was 4% and 6%. The maximum free strain, temperature drop, failure age, failure stress, and failure stress-to-axial tensile strength ratio of concrete increased with increasing dosage of MCEA when the dosage was not more than 4%. The early-age tensile creep of concrete increased with increasing dosage of MCEA. The rate of tensile stress and cracking failure potential of concrete evaluated by integrated criterion decreased with increasing dosage of MCEA when the dosage of MCEA was not more than 4%, but increased with increasing dosage of MCEA from 4% to 6%. A simplified stress-strain failure criterion based on the results of tensile strength, modulus of elasticity, and restrained cracking tests was proposed for estimating the safety of concrete under uniaxial restrained condition.