Early Strength Agent Research Articles

A high temperature composite cement for geothermal application

In the process of geothermal reservoir exploitation, the performance of cementing material in high temperature environment is the key to ensure the quality of cemented casing for wall protecting and leakage plugging or effective zonal isolation. Based on a systematic approach of theoretical analysis, experimental research and microscopic analysis, this paper presents a new Nano SiO2-basalt fiber composite cement (NSBF) for application in geothermal reservoir exploitation. The NSBF consists of a modification of Class G oil-well cement with optimized additions of fly ash, Nano SiO2, basalt fiber, early strength agent (ZQ), and a water reducing agent (GB). The physical properties of the NSBF (fluidity, pump-ability, setting time and compressive strength), obtained by carefully prepared lab tests, were shown to be suitable for high temperature application. Finally scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to analyze the micro characteristics for an interpreted hydration mechanism of NSBF at high temperature. Our study results may provide a new product for a quality cementing material or better zonal isolation material in the exploitation of geothermal reservoir.

Effect of Magnesium Carbonate on Hydration and Hardened Properties of Portland Cement Paste

The effects of magnesium carbonate on the setting time and compressive strength of Portland cement paste were studied when the content of magnesium carbonate was 0wt%, 0.5wt%, 1wt%, 2wt%, and 3wt% by the weight of cement. The influence mechanism was analyzed through combining with the tests of hydration heat, X-ray diffraction (XRD), differential thermal analysis-thermogravimetric analysis (DTA-TG), and scanning electron microscope (SEM). The results show that magnesium carbonate makes the setting time of cement paste shorten, and makes the compressive strengths of cement paste increase at 1 day and 7 days, but decrease at 28 days. The testing results of the heat of hydration, XRD, SEM, and DTA-TG show that magnesium carbonate promotes the formation of Ettringite (AFt) and the hydration of calcium silicate in the early stage when its content is less than 1wt%, but the addition of magnesium carbonate is unfavorable to the later hydration of Portland cement. Based on the above analysis, it is suggested that the content of magnesium carbonate is not more than 1wt%, which has good reference value for using magnesium carbonate to prepare early strength agent for cement paste.

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

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.

Early-age strength property improvement and stability analysis of unclassified tailing paste backfill materials

High-density tailings, small cementitious materials, and additives are used for backfill materials with poor early compressive strength (ECS), which may greatly affect the mining and backfill cycle, to prepare paste backfill materials (PBMs) with a high ECS. The effects and mechanisms of different early strength agents on the property of PBM are investigated. The action mechanism of additives on the properties of PBM is also analyzed through X-ray diffraction, scanning electron microscope, and energy dispersive spectrometry. Results show that the effects of single-component additives 1, 3, and 6 are better than those of the other additives, and their optimal dosages are 3wt%, 1wt%, and 3wt%, respectively. The optimum multicomponent combinations are 1wt% of additive 1 and 1.5wt% of additive 6. The ECS of the paste with additive 10 increases to a greater extent than that of the other pastes because of the synergistic action of additive 1 with additive 6. The hydration product of Ca(OH)2 is consumed, and more C-S-H gels are generated with the addition of additives to paste. Tailings particles, ettringite crystals, and gels intertwined with one another form a dense net-like structure that fills the pores. This structure can significantly improve the ECS of PBM.

A High Thermal Conductivity Cement for Geothermal Exploitation Application

In geothermal reservoir exploitation, the thermal conductivity of casing cement material is a key parameter that may affect the heat exchange and utilization efficiency of geothermal reservoirs. Based on a systematic approach of theoretical analysis, experimental research and microscopic analysis, this paper presents graphite composite cement (GC) with high thermal conductivity for potential application in geothermal reservoir exploitation. The GC consists of ordinary Portland cement (P.O 42.5), natural flake graphite, water-reducing agent (GB), early strength agent (CaCl2) and defoamer (HB-03). The physical properties of the GC, such as fluidity, pumpability, setting time, compressive strength and thermal conductivity, were obtained by carefully prepared laboratory tests that met our expectation. Finally, X-ray diffractometry and environmental scanning electron microscopy were used to analyze the micro-characteristics for an interpreted thermal conduction mechanism of GC. The results of analyses show that the formation of thermal conductivity network of natural flake graphite in cement is a key to improve thermal conductivity. The research results provide a new solution to the problems of low thermal energy extraction efficiency and poor cementing quality of geothermal reservoirs.

The Effects of Fineness and TEA-Based Chemical Admixture on Early Strength Development of Concrete in Construction Site Applications.

This study examines effects of cement fineness and chemical admixtures of early strength agents on the early strength development of concrete. Three cement types were selected, namely ASTM type-I ordinary Portland cement (OPC), fineness ordinary Portland cement (FOPC), and ASTM type-III early Portland cement (EPC), and the mixing proportions of concrete were set by adding a triethanolamine-based chemical admixture to FOPC. The evaluation items considered in this study included raw material analysis, compressive strength, and maturity (D∙h). The time required for the development of concrete strength of 5 MPa in the three cement types was estimated and compared. The results revealed that using FOPC enhances the strength development of concrete owing to its higher fineness and SO3 content compared to OPC. In addition, it has been observed that using both FOPC and TCA yields a similar performance to that observed using EPC, in light of the improved early strength development at low temperatures.

Effect of early strength agents on specified density concrete

Early strength agents are beneficial to improving early strength of concrete, thereby shorting curing time as well as production efficiency of concrete products, and consequently saving production costs. This study investigated the influence of triethanolamine, potassium carbonate, Calcium formate and Potassium aluminum sulfate on properties of specified density concrete, based on orthogonal experiment, composite early strength agent is determined.

Effects of chloride on the early mechanical properties and microstructure of gangue-cemented paste backfill

The addition of an early strength agent as an additive in cement-based materials provides several security-related, technical, and economic advantages, such as improving the early strength of the paste and accelerating the cycle frequency of mining and filling. In this paper, we present the results of an experimental investigation of the effects of chloride on the early age (3, 7, and 28 days) strength of gangue-cemented paste backfill (GCPB). The GCPB specimens had an initial chloride concentrations of 0‰, 5‰, 10‰, 20‰, 30‰, and 40‰, and the obtained samples were analyzed by performing uniaxial compressive strength tests, X-ray diffractometry, scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The results show that chloride significantly affects the early-age strength of GCPB. At early ages, chloride can have positive and negative effects, i.e., the GCPB strength increased with an initial chlorine content of 10‰, while it decreased for GCPB with an initial chlorine content of 40‰. These positive or negative effects depend primarily on the initial concentration of chloride in the GCPB. The key reason for this characteristic is the promotion or suppression of cement hydration by chloride ions. The essential factor that affects the GCPB strength is the relationship between the volume of voids and the amounts of calcium silicate hydrate gel, ettringite, and Friedel's salt formed. These results indicate that it is important to consider the influence of chloride on the early strength of GCPB to improve the self-stabilizing strength of GCPB and the economic benefits of coal mines.

Preparation of nano-calcium silicate hydrate and its application in concrete

The calcium silicate hydrate (C-S-H) is the most important hydration product of cement hydration and the most critical source of strength for concrete. In this paper, nano-calcium silicate hydrate was synthesized by sol-gel method. The results show that the nano-calcium silicate hydrate prepared by high-speed stirring and under the action of specific dispersant solution at 40 °C has the smallest particle size and the best dispersion. The early strength of concrete can be improved by adding nano-calcium silicate hydrate as early strength agent. It can reduce its nucleation energy barrier, promote cement hydration, thereby significantly shortening the setting time of concrete, and greatly improving the compressive strength and flexural strength.

Role of swelling agent and set-controlling admixtures on chloride binding and diffusion in cement matrix

Chloride binding and diffusion was investigated for cement matrix with swelling agent (SA), early-strength agent (ESA) and set-retarding agent (SRA). Chloride binding isotherms (CBIs), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and thermodynamic modeling were applied to quantitatively reveal the mechanisms of chloride binding. The current results indicate that ESA will reduce chloride binding capacity and enhance chloride diffusivity due to the competition between sulphate and chloride. SRA holds a reverse regularity on account of increasing long-term hydration degree. The role of SA combines with kaolin and gypsum, resulting in a slighter reduction of chloride binding capacity.

Effect of brucite fibers and early strength agent on cement stabilized macadam in Alpine regions

This paper aims to study the mechanical performance and durability properties of the brucite fiber reinforced cement stabilized base at the low-temperature condition. Five type samples with different fiber content were prepared, and the related mechanical performance and durability properties were examined. The test results indicated that the added brucite fiber could enhance both the mechanical and durability performance of the cement stabilized base. Specifically, it was found that the unconfined compressive/splitting tensile strength can reach at 3-day age and 7-day age could reach 41%/37% and 67%/67% respectively compared to the results at 28-day age. Furthermore, the added brucite fiber can reduce the drying shrinkage of the cementitious material and also improve its resistance to frost damage. The X-ray diffraction and Scanning Electron Microscopy tests were further conducted to examine the improvement mechanism of the brucite fiber reinforcement. It is found that the hydration degree of cement paste was enhanced with the added brucite fiber. The designed brucite fiber cement stabilized sample in this study is suitable for pavement construction in alpine regions.

Preparation, properties and hydration process of low temperature nano-composite cement slurry

In the process of drilling gas hydrate in permafrost regions, the performance of cement slurry in low temperature is crucial to the control of wall protecting and leakage plugging in a borehole. In this research, the preparation, properties and hydration process of nano-composite cement (NC) in low temperature were comprehensively investigated by a combined method of theoretical analysis and experimental approach. In terms of the “synergistic hydration” effect induced by the compounding of ordinary Portland cement with sulphoaluminate cement, NC which aimed at stabilizing borehole in gas hydrate drilling in low temperature, it introduced sets of compositions of water reducing agent (JSS), early strength agent (LC), antifreeze agent (CC) and nano materials (SiO2) to examine its physical properties, such as rheology, fluidity, pumpability, setting time and compressive strength by lab tests. An integrated analysis of hydration exotherm, X-ray diffraction and scanning electron microscopy was used to pattern the low temperature hydration process of NC, and then it concluded a low temperature hydration process model to NC. The research results provide a scientific basis for promoting the application research of NC in low temperature, and provide a new solution for wall protecting and leakage plugging in the drilling of natural gas hydrate in permafrost regions.

Water-blocking nano-composite cement-based grouting materials

With the rapid development of underground engineering construction such as hydropower projects, mines, tunnels, etc., underground hydrodynamic-related problems have become a more prominent challenge. In view of the shortcomings of the current hydrodynamic grouting materials, a systematic analysis for the preparation, performance, and water-blocking reinforcement mechanism of a new nano-composite cement-based dynamic water grouting material was carried out by a comprehensive approach of theoretical analysis, laboratory test, field test, and microscopic study. Utilizing the “synergistic hydration” effect produced by compounding ordinary Portland cement and sulfoaluminate cement, aimed at the harmonization of rheological and solidification characteristics of grouting material, a new nano-composite cement-based grouting material (NCC) was developed by mixing with water-reducing agent (JC), early strength agent (VT), nano-materials (SiO2), and cellulose (QC). The properties of the NCC, such as rheology, fluidity, pumpability, setting time, compressive strength, and anti-scour performance were carefully examined by laboratory tests. The NCC product was successfully field tested. Finally, an integrated analysis of X-ray diffraction and scanning electron microscopy was used to investigate the mechanism of water-blocking reinforcement, and consequently, it led to a water-blocking reinforcement process model of nano-composite cement slurry. The research result, i.e., NCC product, provided a new solution to effectively resolve the problem of gushing water disaster in the management of underground engineering construction.

Effect of freezing and thawing cycle properties of cement-stabilized macadam materials with self-prepared early-strength agents

Three types of cement-stabilized macadam materials and raw materials mixed with a self-made early-strength agent were prepared and subjected to freeze-thaw cycle tests. Based on the unconfined compression and freeze-thaw cyclic tests, the compressive strength and mass loss rate, and frost resistance coefficients of these samples were assessed and compared. The change of material properties caused by different content of early-strength agent was analyzed. The results show that three kinds of early-strength agents can improve the compressive strength and freezing resistance of cement-stabilized macadam. The compressive strength of cement-stabilized macadam with 2.0% anhydrous sodium sulfate and 1.0% triethanolamine is the best; the compressive strength is increased by 73.8%. Cement-stabilized macadam material with 1.5% anhydrous sodium sulfate and 1.0% triethanolamine has the best frost resistance, and its mass loss rate is reduced by 0.733%. The curves of mass loss rate and freeze-thaw cycle times of four groups of material are established, and the trend of positive correlation between the content of anhydrous sodium sulfate and the freezing resistance is obtained.

Analysis of Active Mechanism of Chemical Activated Strontium Slag

In order to improve the activity of strontium slag, the mixed cementitious material of strontium slag cement was prepared by adding 30% (mass fraction) of pulverized strontium slag into cement. Chemical activators such as Na2SiO4, NaOH, CaCl2, NaCl, Ca(OH)2, Na2SO4 were added to the cementitious material. The flexural and compressive strength values of 3d, 7d, 28d were obtained by mortar strength test, and were used as the base with standard samples. The mechanism of activator improving the activity of strontium slag is analyzed. CaCl2 and NaCl are cement early strength agents. So the substitution of strontium slag with silica powder is compared. The strength of strontium slag is judged by principle analysis. The results show that NaOH and Ca(OH)2 are beneficial to the activation of SiO2 and Al2O3, but the amount of ettringite is large and the strength is reduced, so there is a certain active excitation for strontium slag, but the effect is not very good; the addition of Na2SiO4 causes damage to volume stability and it is the worst of all activators. the compressive strength increases rapidly in 3d and 7d after adding NaCl, so it is mainly to stimulate the early strength of cement; The 28d compressive strength of strontium slag cement containing CaCl2 is higher than that of strontium slag cement containing other chemical activators, which can reach 91% of the compressive strength of cement mortar. It is preliminarily judged that CaCl2 has an exciting effect on strontium slag and the exciting effect is obvious.

Effect of sulfide on the long-term strength of lead-zinc tailings cemented paste backfill

With the production of a large amount of metal tailings, backfill is one of the best models for waste management and has been widely used in many mines. Metal deposit, especially lead-zinc mines, usually contain sulfide minerals, mainly pyrite. Sulfide attack would cause the strength degradation of cemented materials and decrease the structural stability. This study aimed to understand the effect of sulfide on the long-term strength of lead-zinc tailings cemented paste backfill (CPB). CPB specimens with four sulfur contents (2 wt%, 5 wt%, 10 wt%, 15 wt%) were prepared to investigate their physicochemical characteristics in 28–360 days. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) analyses of the CPB specimens were also conducted to obtain valuable information. The results showed that the highest strength of CPB was achieved at curing 90 days. Sulfide showed early strength agent property and the early strength of CPB with sulfur content of 5 wt% was improved. The internal system of CPB was alkaline, and sulfate mainly involved in cement hydration reaction. SEM observed that CPB specimens had compact structures, and calcium silicate hydrate (C-S-H) was produced. After 90 days, under the influence of sulfide, the strength of all the CPB specimens decreased, and the strength of CPB specimen with the highest sulfur content decreased the most. The pH value of the solution continuously decreased and eventually became acidic. A large amount of sulfate accumulated. The hydrated calcium silicate decomposed in the acidic environment. The number of expansive ettringite and gypsum products increased, and the number of large pores increased. Sulfide reactivity includes sulfate and acid attack. Large internal defects lead the strength and stability deterioration. This study compared the differences between sulfide erosion and sulfate attack, then provided some advice for the disposal of high sulfide tailings.

Study on early strength agent for improving early strength performance of water-stabilized macadam material

Because triethanolamine (TEA) and anhydrous sodium sulfate (Na2SO4) can both improve the performance of cement stabilized macadam material, an optimal dosage group is found by compounding the two materials to improve the dry shrinkage performance of cement stabilized macadam material. Based on unconfined compression test and dry shrinkage strain test, the changes of compressive strength of water-stabilized macadam materials caused by different compound dosage groups and original materials were compared. The results show that the three dosage groups can improve compressive strength and reduce the dry shrinkage strain of the cement stabilized macadam material. The compressive strength of 2.0 % anhydrous sodium sulfate and 1.0 % triethanolamine was the best, increasing 73.8 %; moreover, the dosage group can effectively reduce shrinkage cracks, which is 3.88 % less than that of the blank control group. The test data were tested by correlation analysis and there were significant differences between the control group and each dosage group, which indicated that the admixture had a significant improvement on the material properties.

The effect of Al2(SO4)3 + Li2CO3 + C6H15O3N compound early strength agent on the early mechanical properties of concrete

The effect of Al2(SO4)3 + Li2CO3 + C6H15O3N compound early strength agent on the early mechanical properties of concrete is studied in this paper, the microanalysis was carried out by SEM scanning electron microscope. The results showed that Al2(SO4)3 + Li2CO3 + C6H15O3N composite early strength agent had very significant enhancement effect. The flexural strength of concrete reaches 7.9MPa for 8 hours, and the compressive strength is 43.06MPa, which is increased by 648% and 259% respectively, compared with those without the early strength agent.

Experimental study on selection of early-strength agent for low-strength cementitious materials prepared with manganese tailings

The early-strength characteristics and mechanism of eight kinds of early-strength agents in low-strength cementitious materials prepared with manganese tailings were studied, and then the optimum mixing amount was obtained by means of progressing and superimposing optimization. The phase composition and morphology of hydration products were characterized through X-ray diffraction and scanning electron microscopy. The results indicated that there existed good superimposing effect among triethanolamine, ferric chloride and lithium carbonate. When the mixing amount of triethanolamine, ferric chloride and lithium carbonate were 0.04, 0.3 and 0.7%, the compressive strength of 3- and 7-day net paste samples increased by 105.5 and 34.5%, while the porosity of 3- and 7-day decreased by 8.3 and 7.4%, respectively. The initial setting time shortened from 130 to 65 min. Therefore, the combination of early-strength agents could accelerate the dissolution of tailings, shorten hydration cycle, increase the amount of ettringite and calcium silicate hydrate, compact the internal structure further, reduce the porosity, which could achieve the compressive strength improved in short time.

Steel-Corrosion Characteristics of an Environmental Inhibitor using Limestone Sludge and Acetic Acid

Calcium acetate, which can be used in concrete to shorten the construction period and to improve productivity, was manufactured using limestone sludge and acetic acid. Calcium acetate contains a carboxyl group, and it can provide anticorrosive properties by forming a complex with the steel surface. We evaluated the basic performance of a carboxylic early-strength agent produced from industrial by-products (limestone sludge and acetic acid) as a corrosion inhibitor. A comparative evaluation was performed using calcium nitrate, which is a conventional early-strength agent; the corrosion area ratio, corrosion state, and electrochemical performance of a steel plate immersed in aqueous solutions were evaluated. A steel plate immersed in calcium acetate was not substantially corroded. The electrochemical investigations showed a high corrosion potential based on the impedance characteristics. The corrosion current showed anodic values, and no corrosion occurred on the surface of the steel plate because of the adsorption of carboxyl groups. Scanning electron microscopy indicated that the steel plate was covered by a crystalline coating, which suppressed corrosion. We show that it is possible to develop an environmentally friendly recycling method as an early-strength agent and corrosion inhibitor when manufacturing calcium acetate using limestone sludge.