Use of nano-silica to increase early strength and reduce setting time of concretes with high volumes of slag

The effect of calcium nitrate (CN) dosages from 0 to 3% (of cement mass) on the properties of fresh cement paste rheology and hardening processes and on the strength of hardened concrete with two types of limestone-blended composite cements (CEM II A-LL 42.5 R and 42.5 N) at different initial (two-day) curing temperatures (−10 °C to +20 °C) is presented. The rheology results showed that a CN dosage up to 1.5% works as a plasticizing admixture, while higher amounts demonstrate the effect of increasing viscosity. At higher CN content, the viscosity growth in normal early strength (N type) cement pastes is much slower than in high early strength (R type) cement pastes. For both cement-type pastes, shortening the initial and final setting times is more effective when using 3% at +5 °C and 0 °C. At these temperatures, the use of 3% CN reduces the initial setting time for high early strength paste by 7.4 and 5.4 times and for normal early strength cement paste by 3.5 and 3.4 times when compared to a CN-free cement paste. The most efficient use of CN is achieved at −5 °C for compressive strength enlargement; a 1% CN dosage ensures the compressive strength of samples at a −5 °C initial curing temperature, with high early strength cement exceeding 3.5 MPa but being less than the required 3.5 MPa in samples with normal early strength cement.

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Several Common Retarders on Performance of Ultra-Early-Strength Grouting Material

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.477-478.931 ◽

2013 ◽

Vol 477-478 ◽

pp. 931-935

Author(s):

Chang Zheng Sun ◽

Xiao Ping Zhang ◽

Hai Nan Zhao ◽

Qiang Gao

Keyword(s):

Mechanical Strength ◽

Setting Time ◽

Strength Properties ◽

Preliminary Screening ◽

Final Setting Time ◽

Grouting Material ◽

Early Strength

To explore retarders on performance of ultra-early strength grouting material, Retarder, which are commonly used in the market after a preliminary screening, are further tested and analyzed for initial fluidity, setting time and mechanical strength properties of super early strength grouting material. The results show that: When borax content is 0.4%, the initial fluidity, final setting time, workability, mechanical strength are the best.

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Optimization and Hydration Mechanism of Composite Cementing Material for Paste Filling in Coal Mines

Advances in Materials Science and Engineering ◽

10.1155/2019/3732160 ◽

2019 ◽

Vol 2019 ◽

pp. 1-13

Author(s):

Jinxiao Liu ◽

Wenxin Li ◽

Feng Zhang ◽

Xinguo Zhang ◽

Lianjun Chen ◽

...

Keyword(s):

Early Stage ◽

Uniform Design ◽

Setting Time ◽

Coal Mines ◽

Hydration Products ◽

Hydrated Calcium Silicate ◽

Sulphoaluminate Cement ◽

Final Setting Time ◽

Early Strength ◽

Cementing Material

The low early strength of materials for paste filling in mines caused by low early strength of composite cementing material has been a severe issue. In this study, the effects of sulphoaluminate cement and gypsum on strengths of composite cementing material were investigated experimentally by employing the constrained formulation uniform design. With the content of the sulphoaluminate cement below 14% and the content of the gypsum below 16%, the compressive strengths of composite cementing materials increased, especially early strength. However, the initial and final setting time does not meet the engineering requirements in this case. Optimization tests of composite additives demonstrated that H2BO3(0.3%) + Na2SO4(0.1%) and H2BO3(0.3%) + NaNO2(0.1%) were ideal setting retarding and early strengthening composite additives as they can both reduce the initial and final setting time and enhance compressive strengths of composite cementing material. Investigations by XRD and SEM revealed that the hydration products of composite cementing material were dominated by AFt (ettringite) at the early stage and by C-S-H (hydrated calcium silicate) gel + CH (calcium hydroxide) gel at the middle and late stages. The hydration products of ratio-optimized composite cementing material do not restrain each other due to the generation sequence. Instead, they grew interactively and were coupled, thus facilitating the growth of the hardened body. This study can provide references for optimization of composite cementing material for paste filling in coal mines.

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Research on Mining Water-Rich Fly-Ash-Based Filling Material

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.988.201 ◽

2014 ◽

Vol 988 ◽

pp. 201-206 ◽

Cited By ~ 1

Author(s):

Wei Xin Chen ◽

Feng Yi Li ◽

Xian Hua Guan ◽

Lei Chen ◽

Wen Bo Nie

Keyword(s):

Fly Ash ◽

Industrial Waste ◽

Setting Time ◽

Physical And Mechanical Properties ◽

Filling Material ◽

Metal Mine ◽

Early Strength ◽

The Cost ◽

Cementing Material ◽

Early Activity

It had decades of history that cementing material was used for filling in coal mine or metal mine goaf, which was a common filling material in recently filling mining. Paste and high water material have excellent performance, but the price was too high, which restricted the development of cemented filling technology severely. Later, fly ash and other industrial waste were mixed into the cementing material in order to reduce the cost, but because of which early activity was low, the early strength was reduced by mixing too much fly ash and other industrial waste, the setting time was extended, which affected the filling effect seriously. Therefore, it becomes a key problem that how to excite the early activity of fly ash. It was a breakthrough to select the appropriate activator and activation method, because of the difference mechanism of action and effects for different activators of fly ash, the complexity composition of filling material mixed with large number of fly ash, and the early and late physical and mechanical properties [1,2].Four salts are used for activators in this paper, which are mixed with fly ash and water, and a display method was selected to maximum activate the activity of fly ash, increase the early strength of the material, and reduce the cost of the material.

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Research on the Application of Slipform Concrete of Well Tower in winter

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.204-208.3703 ◽

2012 ◽

Vol 204-208 ◽

pp. 3703-3706

Author(s):

Xiang Zong

Keyword(s):

Mechanical Performance ◽

Setting Time ◽

Reducing Agents ◽

Reducing Agent ◽

Mix Proportion ◽

Time Test ◽

Early Strength ◽

Blend Ratios

To meet the demand of performance of slipform concrete in a well tower in winter, different blend ratios of early strength water reducing agents were added to the concrete. Compared with reference concrete, their setting time test analyses, workability analyses and tests of mechanical performance and removal of forms were conducted in the laboratory. The results show that concrete with FS-A early strength water reducing agent can greatly improve early strength of concrete and meet the demand of relevant performance of slipform. This research may provide reference for design of mix proportion and construction in similar slipform project.

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Development of Coal Mine Filling Paste with Certain Early Strength and Its Flow Characteristics

Geofluids ◽

10.1155/2021/6699426 ◽

2021 ◽

Vol 2021 ◽

pp. 1-14

Author(s):

Feng Zhang ◽

Jinxiao Liu ◽

Haiming Ni ◽

Wenxin Li ◽

Yongle Liu

Keyword(s):

Fly Ash ◽

Coal Mine ◽

Setting Time ◽

Flow Characteristics ◽

Coal Gangue ◽

Practical Significance ◽

Range Analysis ◽

Factors Affecting ◽

Early Strength ◽

Backfill Strength

In coal mine paste filling technology, geomaterials like coal gangue and fly ash are used as the main component, and cement is applied as the cementing material. In the mining production, mining-and-filling is a cyclic work, where the filling immediately after mining and mining immediately after filling. Long solidification time after filling will affect mining; consequently, the paste should have early strength. In addition, the prepared paste will be conveyed to goaf through the pipeline. The paste flow characteristics will change to some extent in the conveying process, and there is uncertainty about whether the paste can meet the requirements of pumpability and strength. Therefore, the influence of pipeline conveying on flow characteristics of paste before filling the goaf should be taken into consideration. Based on the above two points, this paper studies the paste strength, backfill strength, and pumpability parameters in coal mine paste filling and determines the early and later strength of coal mine paste, as well as the pumpability parameters such as slump degree, segregation degree, setting time, and paste gradation. With the determined mass proportion of coal gangue, fly ash, and silicate cement, the orthogonal test was carried out with three factors including gypsum content, the content of early strength agent (Na2SO4), and the mass concentration, and at three levels. The factors affecting paste flow characteristics were determined by range analysis, and the factors affecting the paste’s early strength were determined by the XRD test and SEM test on its microstructure. With paste proportioning and pipeline conveying simulation system, taking slump, segregation degree, backfill strength, and other parameters as indicators, we obtain the influence law of pipeline conveying on the flow characteristics of paste. The research has great theoretical and practical significance for developing coal paste with early strength and its flow characteristics.

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Effect of nano-silica as cementitious materials-reducing admixtures on the workability, mechanical properties and durability of concrete

Nanotechnology Reviews ◽

10.1515/ntrev-2021-0097 ◽

2021 ◽

Vol 10 (1) ◽

pp. 1395-1409

Author(s):

Changjiang Liu ◽

Xin Su ◽

Yuyou Wu ◽

Zhoulian Zheng ◽

Bo Yang ◽

...

Keyword(s):

Mechanical Properties ◽

Building Materials ◽

Setting Time ◽

Microscopic Analysis ◽

Chloride Ion ◽

Cementitious Materials ◽

Hydration Reaction ◽

Ion Permeability ◽

Nano Silica ◽

Durability Of Concrete

Abstract Nano-silica (NS) is one of the most important nanomaterials in recent years. It is used as a new cement-based composite reinforcement in building materials because of its high volcanic ash activity. In order to achieve the goal of carbon peaking and carbon neutralization, combined with the research idea of cementitious materials-reducing admixture for concrete, under the condition of reducing the amount of cement in concrete by 20%, the influence of different dosages of NS on the setting time and mechanical properties of concrete was analyzed. In addition, the shrinkage performance, impermeability, and resistance to chloride-ion permeability of concrete were also studied. The results show that under the same curing conditions and ages, when the NS dosage is 2.5%, the compressive strength and splitting tensile strength of the specimen after 28 days of curing are the highest, reaching 40.87 and 3.8 MPa, which show an increase by 6.6 and 15.15%. The shrinkage performance of concrete increases with the increase in NS dosage. In addition, when the NS dosage is 2.0%, the durability of concrete has also been greatly improved. The impermeability of concrete increased by 18.7% and the resistance to chloride-ion permeability increased by 14.7%. Through microscopic analysis it was found that NS can promote the hydration reaction, generate more hydration products such as calcium silicate hydrate (C–S–H), enhance the interfacial adhesion between the matrix and the aggregate, and form a closer interfacial transition zone. Moreover, the addition of NS also reduces the cumulative pore volume in concrete, refines the pore size, and makes the internal structure of concrete denser.

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Effects of Highly Crystalized Nano C-S-H Particles on Performances of Portland Cement Paste and Its Mechanism

Crystals ◽

10.3390/cryst10090816 ◽

2020 ◽

Vol 10 (9) ◽

pp. 816

Author(s):

Yuli Wang ◽

Huijuan Lu ◽

Junjie Wang ◽

Hang He

Keyword(s):

Portland Cement ◽

Cement Paste ◽

Setting Time ◽

Tricalcium Silicate ◽

Strength Development ◽

Early Age ◽

Hydration Products ◽

X Ray ◽

Early Strength ◽

Portland Cement Paste

In order to improve the early age strength of ordinary Portland cement-based materials, many early strength agents were applied in different conditions. Different from previous research, the nano calcium silicate hydrate (C-S-H) particles used in this study were synthesized through the chemical reaction of CaO, SiO2, and H2O under 120 °C using the hydrothermal method, and the prepared nano C-S-H particles were highly crystalized. The influences of different amounts of nano C-S-H particles (0%, 0.5%, 1%, 2% and 3% by weight of cement) on the setting time, compressive strength, and hydration heat of cement paste were studied. The hydration products and microstructure of the cement paste with different additions of nano C-S-H particles were investigated through thermogravimetry-differential thermal analysis (TG-DTA), X-ray powder diffraction (XRD), and scanning electron microscope (SEM) tests. The results show that the nano C-S-H particles could be used as an early strength agent, and the early strength of cement paste can be increased by up to 43% through accelerating the hydration of tricalcium silicate (C3S). However, the addition of more than 2% nano C-S-H particles was unfavorable to the later strength development due to more space being left during the initial accelerated hydration process. It is suggested that the suitable content of the nano C-S-H particles is 0.5%−1% by weight of cement.

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Assessment of Heat Resistant Concrete of Magnesia-Phosphate

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.800.341 ◽

2013 ◽

Vol 800 ◽

pp. 341-344

Author(s):

Lin Chun Zhang

Keyword(s):

Heat Resistance ◽

Refractory Concrete ◽

Setting Time ◽

Potassium Phosphate ◽

Resistant Material ◽

Heat Resistant ◽

Repair Materials ◽

Heat Resistant Material ◽

Early Strength ◽

Short Setting Time

In this paper, we choose heat resistant material wollastonite and corundum to get the concrete which has heat resistance up to 600 centigrade. SEM reveals that at the temperature of 400 centigrade and 600 centigrade, the material is very dense. But when the temperature gets 800 centigrade and 1000 centigrade, the SEM reveals cracks. The refractory concrete made by magnesium potassium phosphate as the binder and wollastonite and corundum as aggregate has short setting time, early strength and rapid hardening. And it is suitable for emergency repair materials for the kiln.

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