Expansive Agent Research Articles

Effects of mix proportion and curing condition on mechanical properties of polyvinyl alcohol fibre ECC

With the requirements for the ductility, toughness and durability of structures increasing and the promotion of sustainable development, low-cost and high-performance building materials are highly valued by the engineering community. In this work, 12 groups of engineered cementitious composites (ECC) made with polyvinyl alcohol fibre (PVAF) were prepared. The specimens were divided into two test groups according to the origin of the PVAF: group JK-II (a well-known commercial fibre) and group CL-C (low-cost fibre). Test group JK-II was used to study the effect of waste glass powder on uniaxial tensile and thin-plate flexural properties. The CL-C test group was used to study the coupled effect of curing condition and expansion agent on uniaxial tensile and flexural properties. The PVAF-ECC prepared in this study all showed good tensile and flexural properties. The enhanced effect of JK-II fibre on the uniaxial tensile and flexural properties of the PVAF-ECC was analysed and the advantages and disadvantages of the materials used in groups JK-II and CL-C were comprehensively investigated. Future research directions and application suggestions for the PVAF-ECC are introduced.

Synergistic effect of shrinkage mitigating materials on rheological properties of flowable and thixotropic cement paste

This study investigates the effect of individual and combined additions of CaO-based expansive agent (EA), shrinkage reducing admixture (SRA), and super absorbent polymer (SAP) on key characteristics of flowable cement paste mixtures proportioned with a water-to-cement ratio of 0.40. Of special interest is the effectiveness of these admixtures to mitigate shrinkage of cementitious materials for 3D printing. Static and dynamic yield stress, plastic and apparent viscosities, and thixotropy were evaluated at 20-min intervals up to 90 min. Compressive strength development and autogenous shrinkage were also determined. A factorial design approach was developed to evaluate the synergetic effects of the shrinkage mitigating materials (SMM) on performance. Test results showed that the use of any given SMM increases the static and dynamic yield stress, plastic viscosity, and thixotropy. The individual use of SRA and the combination of EA-SRA presented the highest effect on reducing 20-min plastic viscosity and dynamic yield stress, respectively. The combinations of EA-SAP almost tripled the 90-min static yield stress. The individual or combined use of the SMM, especially EA and SAP, significantly reduced autogenous shrinkage. Such systems, however, reduced the 28-d compressive strength by 14%–65%. The lowest value was obtained with the paste made with EA-SRA. A multi-objective optimization based on the measured properties was performed. The results revealed that the use of 10% EA either with 0.125% SAP or 1% SRA can result in producing flowable and thixotropic cement paste with high pumpability and buildability for 3D printing applications, no autogenous shrinkage, and high strength.

Experimental study of a self-expanding filling material for mine-sealing walls

A self-expanding filling material for mine-sealing walls (SEFM-MSW) was developed to solve the problems of the current main filling materials of MSW, such as high consumption of materials, high labour intensity and poor sealing effects. The material composition and structure were examined in this work and it was found that the performance of the SEFM-MSW was optimised with the addition of an expansion agent at a dosage of 0.4–1.0%, an admixture (dosage of 1.0–1.5%), fibre (dosage of 0.1%) and a water/cement ratio of 0.45–0.50. The relationship between the 28-day compressive strength and porosity of the SEFM-MSW could be expressed by an exponential function or a power function. The SEFM-MSW compressive strength decreased with an increase in porosity, which is consistent with the Ryshkewitch and Balshin models. The results also showed that when the expansion ratio of the SEFM-MSW was higher, the average pore size was larger, the pore size distribution was wider and the compressive strength was lower. The results of this study have realistic impacts for practical engineering applications.

Application of magnesium oxide expansive agent in hydraulic concrete in China

This paper reviews and summarises the use of magnesium oxide (MgO) in hydraulic concrete in the following projects in China: Baishan hydropower station unexpectedly discovered the beneficial effects of MgO; Dongfeng hydropower station actively used MgO as an expansive agent for the first time in the main project; Changshaba hydropower station used MgO expansive agent for the first time in a full arch dam; Huangjiazhai hydropower station broke through 6% of MgO content for the first time in normal state concrete; and Dahe reservoir broke through 6% of MgO content for the first time in roller-compacted concrete. Findings indicate that the production process, transportation equipment, pouring process, burying of observation instrument, and so on, for concrete mixed with MgO are exactly the same as concrete without MgO. The long-term autogenous volume deformation of MgO concrete presents a good delayed micro-expansion discipline, which matches the long temperature drop process of dam concrete. The use of MgO expansive agent in dam concrete improves concrete's anti-cracking ability, simplifies temperature control measures of dam concrete, speeds up construction progress and saves project investment. At the same time, this paper points out the appropriate quality standards for the MgO expansive agent used in dam concrete and its soundness content that shall not be exceeded.

Preparation and Performance Investigation of Optimized Cement-Based Sealing Materials Based on the Response Surface Methodology.

A new cement-based sealing material, which used Portland cement (PC) as a raw material and supplemented several gel components, such as accelerant, alkali activator, suspension agent, expansion agent, reinforcing agent, was prepared in this work. The effects of these components on the fluidity, setting time, and expansion rate of these sealing materials were investigated by an orthogonal test. The results show that the water–cement ratio and the reinforcing agent content, the accelerant content and the water–cement ratio, and the expansion agent content and the accelerant content are the most important influencing factors on fluidity, setting time, and expansion rate, respectively. In addition, the regression models and response surfaces of the factors were established using a multiple linear regression method. By this means, the influences of the two main factors on each performance of this sealing material were accurately and intuitively reflected for obtaining the optimal value in the optimization area. The results indicate that the sealing materials possess the best performances when the water–cement ratio is 1.1, the accelerant content is 50%, the expansion agent content is 0.1%, and the reinforcing agent content is 3%, which is corresponding to a fluidity of 360–380 mm, an initial (final) setting time of 60 (80)–80 (100) min, and an expansion rate of 2–12%. Furthermore, the microstructures of the optimized sealing material also reveal that the main hydration products of PC are transformed from layered Ca(OH)2 crystals into fine needle-like AFt crystals and C–S–H gels by the promotion effect of the optimizing ratio, thus leading to a more compact structure of optimized cement-based sealing materials.

Effect of CNTs and MEA on the creep of face-slab concrete at an early age

Abstract The creep of face-slab concrete in a rockfill dam is critical for determining the restrained stress and cracking resistance of the concrete at an early age. In this article, the mix proportion of the face-slab concrete for a rockfill dam under construction without any cracking resistance additive was taken as the reference concrete (called JC) mix proportion. The carbon nanotubes (CNTs) and magnesium oxide expansion agent (MEA) were incorporated into JC to prepare face-slab concretes called NC and PC, respectively. The temperature–stress tests under temperature matching curing (TMC) and constant temperature curing (CTC) modes were conducted on these three kinds of concretes to investigate the effects of CNTs and MEA on the early-age creep properties of the face-slab concrete under variable stress conditions. The results showed that the creep performance of NC concrete under CTC mode was lower than that under TMC mode. Combined with mercury intrusion porosimetry test results, the mechanism of the effect of CNTs and MEA on creep was analyzed. The results showed that the temperature change may lead to the CNTs debonding from the cementitious matrix or matrix cracking for the NC concrete. The incorporation of CNTs can increase the early-age creep and improve the cracking resistance of concrete.

Self-Healing Concrete Test Method and Experimental Procedure Conducted on Grout Specimens

Abstract: The concept of self-healing concrete emanated from one of the most prestigious biological properties which is to naturally proceed healing performance when any damage appears and regenerating the functions. Thus, by relating that mechanism in engineering with the common phenomenon of crack formation, this concept has been studied and evaluated over the past years where Self-healing concrete was defined as the ability of cementitious composites to reduce or completely heal a crack width autogenously or autonomously upon damage. Therefore, test method and experimental procedure are conducted to ensure the efficiency of the mechanical properties and performances of the concrete, and also to help in a case of a research work or project; gathering some necessary information or data to apply adequately on a proposed hypothesis or work because the success of experimental research usually confirms that the change observed in the variable under study is solely based on the manipulation of the independent variable. In this paper, the emphasis is highlighted on test method and experimental procedure of self-healing concrete conducted on grout (W), commercial grout with 10% expansion agent (CCSA) and research grout with addition of expansion agent (WCSA) to evaluate its mechanical properties and performances. Keywords: Self-healing, autogenous, autonomous, grout test method.

Biocarbon-directed vertical δ-MnO2 nanoflakes for boosting lithium-ion diffusion kinetics

Manganese dioxide (MnO2) with high theoretical capacity (1230 mAh/g) and low cost is considered as a promising anode material for next generation high energy density lithium-ion (Li+) batteries. However, the intrinsic low electric conductivity and volume change during cycling process limit its applications. In this work, a unique δ-MnO2/C composite has been synthesized through the directed growth of 2D δ-MnO2 nanosheets on the cabbage-leaf-derived biocarbon. The biocarbon acts as both structure buffer to accommodate the volume expansion and conductive agent to promote electron and ion transport. Moreover, oriented δ-MnO2 nanosheets are beneficial for increasing contact area between electrode and electrolyte, thus providing more active sites and shortening the Li+ transmission routes. Electrochemical performances show that δ-MnO2/C displays large reversible capacity (754 mAh/g after 250 cycles at current density of 0.1 A/g), excellent rate capability as well as low charge transfer resistance (17.3 Ω), and high Li+ diffusion rate (DLi+ = 2.91 × 10-14 cm2/s) during the cycles. Furthermore, the density functional theory calculations reveal the lower Li+ migration barrier energies and improved Li+ diffusion kinetics in δ-MnO2/C hetero-layer. This study provides a novel strategy to design advanced nanocomposites, using natural plant-leaf derivatives as structure-directing agents, for the next generation energy storage and conversion systems.

Microstructural phenomena involved in the expansive performance of cement pastes based on type K expansive agent

Certain aspects related to the microstructural mechanisms involved in the expansion performance of cement pastes with ettringite based expansive agent have been analyzed. The possible microstructural mechanisms associated with the shrinkage observed after the maximum expansion is reached along with the influence of the porosity in the expansion obtained were evaluated in order to define the main microstructural mechanism involved in generating the expansion. Different microstructural techniques were considered, while the pore fluid composition evolution was similarly determined. The results obtained indicate that the shrinkage detected after the maximum expansion value should be related to the transformation of low crystalline ettringite in low crystalline monosulfate but the early formation of monocarboaluminate limits this conversion process. Moreover, the main mechanism involved in this expansion obtained is not the diffusion of constituent components from the expansive agent anhydrous grains and further ettringite precipitation, but rather the in-situ precipitation of these components with the subsequent ettringite formation.

Rapid regeneration cement-stabilized macadam: Preparation, mechanical properties, and dry shrinkage performance

Based on the mechanical strength and dry shrinkage of cement mortar, the early strength anti-cracking materials ZFP (mixture of single early strength agents Z1 and Z3 and expansion agent P) and ZSP (mixture of single early strength agents Z1, Z2, and Z3 and expansion agent P) are optimized. Using waste cement-stabilized macadam in road base maintenance as an aggregate, rapid regeneration cement-stabilized macadam containing early strength anti-cracking materials with different contents was prepared, and the mechanical properties and dry shrinkage performances were tested. The early strength anti-cracking mechanism of rapidly regenerated cement-stabilized macadam with different ZSP contents was explored via microscopic experiments. The results show that ZFP and ZSP have an optimal mixing ratio, which makes the setting time, mechanical properties, and dry shrinkage of cement mortar the best. The 2 d compressive strength of rapidly regenerated cement-stabilized macadam containing 8% ZSP was 6.23 MPa, while the 3 d compressive strength of the rapid regeneration cement-stabilized macadam containing 7% ZFP was 6.14 MPa, and the corresponding dry shrinkage coefficients were 91.6% and 11.2% lower than those of the control group, respectively. The chlorine salt, sulfate, and organic amine in ZSP react with calcium hydroxide, which accelerates the hydration process of cement and improves the early strength of rapidly regenerated cement-stabilized macadam. Hydration products, such as expansive sulfuraluminate and chloroaluminate produced by cement hydration in rapidly regenerated cement-stabilized macadam and calcium oxide in ZSP, inhibit early dry shrinkage cracking.

Comprehensive evaluation of self-healing of concrete with different admixtures under laboratory and long-term outdoor expositions

This project presents the evaluation of the self-healing of fibre reinforced concretes containing various admixtures (crystalline admixture CA, expansive agent CSA, superabsorbent polymer SAP) and combinations. They were exposed to several laboratory conditions (water immersion, wet/dry cycles ambient air for 3 months, water flow for 1 week) and to a long-term outdoor exposure for 1 year. Self-healing capacity was assessed by water permeability measurements, mechanical recovery, visual observations and microscopic analyses on the same specimen. This paper presents the mechanical behaviour and microstructure of the healing products, and the correlations with the water permeability measures presented in previous research. The results showed that a high healing of cracks based on water permeability did not necessarily lead to a high mechanical recovery. The highest Strength Regains (109% in average) were obtained for specimens exposed outdoor that presented the lowest Healing Ratios (71% in average). The local density of the healing products may govern the Healing Ratio, while the type of healing products and their extent in the crack depth may control the Strength Regain. Finally, the SAP mix showed overall the best self-healing performance, regarding both durability and mechanical properties.

RETRACTED: Shrinkage and tensile properties of ultra-high-performance engineered cementitious composites (UHP-ECC) containing superabsorbent polymers (SAP) and united expansion agent (UEA)

Ultra-high performance engineered cementitious composites (UHP-ECC) had received extensive attention in recent years in material as well as the field of structural rehabilitation and strengthening due to its excellent mechanical properties, such as high strength and high ductility. However, the high shrinkage is one of the bottlenecks limiting widespread engineering application of UHP-ECC. In this paper, superabsorbent polymers (SAP) and United expansion agent (UEA) were introduced to mitigate UHP-ECC shrinkage. And the effect of different amounts of SAP with UEA on the shrinkage and tensile properties of UHP-ECC are investigate. Results indicate that the incorporation of SAP and UEA can effectively mitigate the autogenous shrinkage, and the autogenous shrinkage decreased with the increasing SAP dosage; however, drying shrinkage had the opposite trend. The incorporation of SAP and UEA improved the tensile ductility of UHP-ECC. The inclusion of SAP reduced the fracture toughness by increasing the matrix porosity, which produced more micro-cracking sources, thus improving the multiple cracking and strain-hardening behaviors of UHP-ECC. Conversely, the incorporation of SAP decreased the fiber/matrix interaction as well as decreasing the effective number of polyethylene (PE) fibers in the cross-section, thus reducing the tensile strength. Finally, pseudo strain hardening index of each specimen was conducted to analyze the effect of SAP with UEA on the tensile properties of UHP-ECC.

Effect of magnesia expansion agent with different activity on mechanical property, autogenous shrinkage and durability of concrete

The addition of Magnesia Expansion Agent (MEA) to reduce shrinkage of concrete has attracted attention gradually. In this study, three types of MEA with different activity, i.e. R, M, and S were added into concrete by 5% weight of cement. The effects of MEA on hydration, mechanical properties, shrinkage and durability of concrete were comprehensively evaluated. The results indicated that MEA has a certain delaying effect on hydration of cement and the effect is related to its activity. The addition of MEA exhibites a larger porosity at early curing age leading to negative effects on the mechanical properties of concrete. Later, the microstructure of concrete is refined due to the micro-expansion of MEA. As a result, the mechanical strength of concrete increases 5–20 % at 84 d. Meanwhile, the autogenous shrinkage of concrete with MEA of type R, M, and S decreases by 47.6 %, 49.7 %, and 23.8 % at 90 d, respectively. Because of the smaller MPPD and lower porosity, concrete with MEA of higher activity presents better resistance to chloride penetration. In addition, the models of shrinkage and chloride diffusion coefficient of concrete with MEA of different activity were proposed and verified, which can be used in the shrinkage and service life prediction of concrete with MEA. Furthermore, with the increase of MEA activity, the frost resistance of concrete decreases. On the contrary, the lower the MEA activity, the lower the sulfate resistance of concrete.

Preparation of cucurbitacin compounds in Siraitia grosvenorii roots by high speed countercurrent chromatography

葫芦素作为四环三萜类化合物广泛存在于葫芦科植物中,但其含量较低、结构相似,采用常规的柱层析分离法较难得到大量、高纯度的单体化合物,导致其活性的研究与应用受到限制。研究采用高速逆流色谱法(HSCCC),建立了一种从罗汉果根提取物中制备葫芦素类化合物的方法。罗汉果根乙醇提取物经HPD-100大孔树脂、MCI、RP-C18柱层析分离后获得葫芦素粗品。通过基于薄层色谱的溶剂选择法(GUESS)对液-液萃取与高速逆流色谱的溶剂体系进行快速筛选,确定采用正己烷-乙酸乙酯-甲醇-水(3:7:3:7, v/v/v/v)萃取葫芦素粗品,有机层萃取物再以正己烷-乙酸乙酯-甲醇-水(4:6:5:5, v/v/v/v)进行HSCCC分离,以上相作为固定相,下相作为流动相,流速2.0 mL/min,主机转速860 r/min,进样量280 mg,一次分离即可获得5种葫芦素类化合物,经高效液相色谱检测其纯度分别为97.0%、95.4%、96.3%、91.6%和95.3%,并通过核磁共振技术、高分辨质谱技术及文献资料对比对各化合物的结构进行鉴定。经鉴定,5种化合物分别为葫芦素Q1、23,24-二氢葫芦素F-25-乙酸酯、葫芦素B、23,24-二氢葫芦素B和二氢异葫芦素B-25乙酸酯。该方法操作简单、快速,分离效果好,可作为规模化制备葫芦素类化合物的一种新方法。

Influence of CaO-based expansive agent, superabsorbent polymers and curing temperature on pore structure evolution of early-age cement paste

Influence of CaO-based expansive agent, superabsorbent polymers and curing temperature on pore structure evolution of early-age cement paste

Experimental Research on the Mechanical Properties and Autogenous Shrinkage of Precast Members Joint Concrete

In the precast building structure, the joint is the key part that affects the mechanical performance of the assembly structure. By selecting coarse and fine fraction aggregate; adding high quality mineral admixture, expansive agent, and water-reducing agent; and optimizing the mixture ratio design, precast members joint concrete (PMJC) with self-compacting performance, micro-shrinkage, good volume stability, and strength matching with precast concrete is developed. In this study, the PMJC with a water-binder ratio, fly ash, ultra-fine silicon powder, sand rate, expansive agent, and water-reducing agent of 0.38, 30%, 3%, 47.7%, 8%, and 0.7%, respectively, showed a good workability which could meet the conditions of on-site construction. In addition, the strength matched the precast members, and the PMJC had certain ductility and stability, small early contraction, and met the requirements of the joint material.

Influence of CaO-based expansive agent on chloride penetration resistance of marine concrete

CaO-based expansive agent (CEA) is a high performance expansive agent, which can well compensate for the shrinkage of concrete. However, due to micro-cracks caused by excessive expansion and poor chemical stability and gelling property of additional Ca(OH)2 (expansion product), durability of marine concrete may deteriorate. Therefore, the application of CEA in marine concrete is controversial. In this study, the autogenous deformation, compressive strength, and chloride penetration resistance of marine concretes containing various dosages of CEA were determined, and the influence mechanism of CEA on the chloride penetration resistance was further explored. The results showed that the addition of CEA increased the expansion deformation, chloride diffusion coefficient, and chloride penetration depth and decreased the compressive strength of marine concrete. In addition, as the dosage of CEA increased, porosity increased and chloride binding capacity decreased. Further discussion indicated that the addition of CEA increased the volume of large capillary pore with diameter between 400 and 5000 nm, and decreased the chloride binding capacity due to the increase in the SO3 content, both of which led to the decrease in chloride penetration resistance of marine concrete. However, when the dosage of CEA was not more than 6%, adding CEA can well compensate for the autogenous shrinkage and improve the crack resistance of marine concrete without a relatively small loss of compressive strength (≤8.7%). In addition, for the marine concretes containing CEA, the chloride diffusion coefficients were very small (<1 × 10-12 m2/s). Therefore, adding no more than 6% CEA, marine concrete had good crack resistance and chloride penetration resistance. Hopefully, the outcomes of this research can provide guidance for the application of CEA in marine concrete.

Evolution of the early compressive strength of cement-slag pastes with CaO-based expansive agent

Evolution of the early compressive strength of cement-slag pastes with CaO-based expansive agent

Bio-inspired self-prestressing concrete (SPC) involving basalt fibers and expansive agent

Inspired by muscle structure, the synergy between basalt fibers (BF) and expansive agent (EA) was revealed and utilized for the development of self-prestressing concrete (SPC). When BF and EA were used together, the restraining action of BF against the autogenous expansion of concrete yielded active confining stress, during which fibers were prestressed, producing SPC. The properties of SPC were investigated by varying BF (0–0.6%) and EA (0–3%) contents. The addition of EA and/or BF decreased workability but improved mechanical performance. The strength-workability envelopes revealed the superiority of the combined use of EA and BF, whose synergistic effect was analysed both qualitatively and quantitatively. Possible mechanisms behind their contribution to sample performance were discussed considering passive and active confinements. Scanning electron microscopy images revealed improvement in the fiber-matrix interface with an increase in the amount of EA. This bio-inspired work shall be beneficial to the development of SPC with improved performance.

Pore Structural and Fractal Analysis of the Effects of MgO Reactivity and Dosage on Permeability and F–T Resistance of Concrete

Currently, the MgO expansion agent is widely used to reduce the cracking risk of concrete. The influence of MgO reactivity (50 s and 300 s) and dosage (0, 4 wt.% and 8 wt.%, by weight of binder) on the air void, pore structure, permeability and freezing–thawing (F–T) resistance of concrete were studied. The results indicate (1) the addition of 4–8 wt.% reactive MgO (with reactivity of 50 s and termed as M50 thereafter) and weak reactive MgO (with reactivity of 300 s and termed M300 thereafter) lowers the concrete’s compressive strength by 4.4–17.2%, 3.9–16.4% and 1.9–14.6% at 3, 28 and 180 days, respectively. The increase in MgO dosage and reactivity tends to further reduce the concrete strength at all hydration ages. (2) Permeability of the concrete is closely related to the pore structure. M50 can densify the pore structure and lower the fraction of large capillary pores at an early age, thus it is beneficial for the impermeability of concrete. In contrast, M300 can enhance the 180-day impermeability of concrete since it can densify the pore structure only at a late age. (3) The influence of MgO on F–T resistance is minor since MgO could not change the air void parameters. (5) MgO concretes exhibit obvious fractal characteristics. The fractal dimension of the pore surface (Ds) exhibits a close relationship with the permeability property of concrete. However, no correlation can be found between F–T resistance and Ds.