Effects of fibers on expansive shotcrete mixtures consisting of calcium sulfoaluminate cement,ordinary Portland cement,and calcium sulfate

The mining industry often uses shotcrete for ground stabilization. However, cracking within shotcrete is commonly observed, which delays production schedules and increases maintenance costs. A possible crack reduction method is using expansive shotcrete mixture consisting of calcium sulfoaluminate cement(CSA), ordinary Portland cement(OPC), and calcium sulfate(CS) to reduce shrinkage. Furthermore, fibers can be added to the mixture to restrain expansion and impede cracking. The objective of this paper is to study the effects of nylon fiber, glass fiber, and steel fiber on an expansive shotcrete mixture that can better resist cracking. In this study, parameters such as density, water absorption, volume of permeable voids, unconfined compressive strength(UCS), splitting tensile strength(STS), and volume change of fiber-added expansive mixtures were determined at different time periods(i.e. the strengths on the 28 th day, and the volume changes on the 1 st, 7 th, 14 th, 21 st, and 28 th days). The results show that addition of fibers can improve mixture durability, in the form of decreased water absorption and reduced permeable pore space content. Moreover, the expansion of the CSA-OPC-CS mixture was restrained up to50% by glass fiber, up to 43% by nylon fiber, and up to 28% by steel fiber. The results show that the STS was improved by 57% with glass fiber addition, 43% with steel fiber addition, and 38% with nylon fiber addition. The UCS was also increased by 31% after steel fiber addition, 26% after nylon fiber addition, and16% after glass fiber addition. These results suggest that fiber additions to the expansive shotcrete mixtures can improve durability and strengths while controlling expansion.

Ultra High Early Strength Self-compacting Mortar Based on Sulfoaluminate Cement and Silica Fume

The influences of silica fume and aluminum sulfate on hydration process of sulfoaluminate cement were carried out by ring flow, setting time, hydration heat, XRD and DTG analyses. In addition, mortar mixtures with different functional additives have been studied through compressive strength, flexural strength, volume stability at early age and porosity characterization tests. The results show that the addition of silica fume and aluminum sulfate reduces the fluidity and shortens the setting time of sulfoaluminate cement paste, promoting hydration process and increasing hydration products at early age. In the case of appropriate proportion of mortar, the inclusion of hydroxy propyl methyl cellulose, dispersible polypropylene fiber arid organic silicon kind of defoamer can control segregation and bleeding, improve mechanical strength and volume stability at early age, and modify the pore distribution of sulfoaluminate cement mortar, respectively. The sulfoaluminate cement mortar can carry out gravitational grouting in the absence of outside force, the compressive strength of 2 hours and 24 hours have reached 26 and 58 MPa respectively, and have good micro- expansion and tiny.pore distribution characterization.

Effect of Natural Zeolite on Performance of Sulfoaluminate Cement-based Planting Cementitious Material

This paper aimed to improve the water-retention performance and basic physical properties of sulfoaluminate cement（SAC）-based planting cementitious material. The effect of natural zeolite on the performance of SAC-based planting material was investigated. The water-retention performance, porosity, compressive strength, and alkalinity had been tested and TG-DSC analysis had been adopted in this paper. Experimental results showed that zeolite was effective to improve the water-retention capacity and 10%, 20% and 30% natural zeolite increased the pore volume of the hardened pastes by 10.6%, 26.0%, and 38.6%, especially pore size below 0.1 μm was increased by 9.7%, 26.2% and 17.5%. And 10% zeolite was beneficial to the compressive strengths of cementitious material and 1, 3, and 28 d compressive strength reached up to 35.9, 55.0, 80.3 MPa. Furthermore zeolite decreased the alkalinity of pore fluid of hardened cementitious material, while the addition of zeolite reached up to 30%, the alkalinity of pore fluid of hardened cementitious material decreased by 8.9%. Therefore zeolite was suitable for improving the performance of SAC-based planting cementitious material.

Effect of Superplasticizers on the Early Age Hydration of Sulfoaluminate Cement

The effects of two types of superplasticizers on the properties of CSA cement pastes during early hydration were studied. The influences of two types of superplasticizers on the properties of cement pastes, including the normal consistency, setting time, fl uidity, and compressive strength, were investigated by using various methods. The hydration products of the cement pastes cured for 1 day and 3 days were studied by X-ray diffraction（XRD） and scanning electron microscopy（SEM）. The results show that the PCE type superplasticizer retards the early age hydration while the FDN type superplasticizer accelerates the early age hydration of the CSA cement. Both types of superplasticizers have no infl uence on the further hydration of CSA cement, confi rmed by the calorimeter tests as well. The ultrasonic pulse velocity measurements were used to probe the influence of two types of superplasticizers on the hydration of CSA cement pastes at a high water-cement ratio（0.45）. The results show that the PCE type superplasticizer retards the early age hydration of the CSA cement while the FDN type superplasticizer has little infl uence on the early age hydration of the CSA cement.

DEVELOPMENT OF COLORED SULFOALUMINATE CEMENT

One process for producing new type colored sulfoaluminate cement is introduced in this paper. The color stability is an important quality index of colored cement products. Kxperimental results show thds cement clinker can be obtained at 1250~1350? by using some industrial refuse as coloration agent, and the products of this cement do not only have a rapid development in strength but also are almost color fast over 3 years.

Extending blending proportions of ordinary Portland cement and calcium sulfoaluminate cement blends:Its effects on setting,workability,and strength development

This study extended blending proportion range of ordinary Portland cement(OPC)and calcium sulfoaluminate(CSA)cement blends,and investigated effects of proportions on setting time,workability,and strength development of OPC-CSA blend-based mixtures.Thermogravimetric analysis(TGA)and X-ray diffraction(XRD)were conducted to help understand the performance of OPC-CSA blend-based mixtures.The setting time of the OPC-CSA blends was extended,and the workability was improved with increase of OPC content.Although the early-age strength decreased with increase of OPC content,the strength development was still very fast when the OPC content was lower than 60%due to the rapid formation and accumulation of ettringite.At 2 h,the OPC-CSA blend-based mortars with OPC contents of 0%,20%,40%,and 60%achieved the unconfined compressive strength(UCS)of 17.5,13.9,9.6,and 5.0 MPa,respectively.The OPC content had a negligible influence on long-term strength.At 90 d,the average UCS of the OPC-CSA blend-based mortars was 39.2±1.7 MPa.

Experimental study and field application of calcium sulfoaluminate cement for rapid repair of concrete pavements

The fast-track repair of deteriorated concrete pavement requires materials that can be placed, cured, and opened to the traffic in a short period. Type III cement and Calcium Sulfoaluminate （CSA） cement are the most commonly used fast-setting hydraulic cement （FSHC）. In this study, the properties of Type III and CSA cement concrete, including compressive strength, coefficient of thermal expansion （CTE） and shrinkage were evaluated. The test results indicate that compressive strength of FSHC concrete increased rapidly at the early age. CSA cement concrete had higher early-age and long term strength. The shrinkage of CSA cement concrete was lower than that of Type III cement concrete. Both CSA and Type III cement concrete had similar CTE values. Based on the laboratory results, the CSA cement was selected as the partial-depth rapid repair material for a distressed continuously reinforced concrete pavement. The data collected during and after the repair show that the CSA cement concrete had good short-term and long-term performances and, therefore, was suitable for the rapid repair of concrete pavement.

Performance development of styrene-butadiene copolymer-modified calcium sulfoaluminate cement mortar under different curing conditions

The purpose of this study was to investigate the change in the physical and mechanical properties of styrene-butadiene copolymer(SB)dispersion-modified calcium sulfoaluminate(CSA)cement mortar as it aged from 28 to 360 d,and cured at different temperatures and relative humidities.The results show that the mechanical properties of reference mortar(RM)of CSA cement,including its flexural,compressive,and tensile bond strength,showed a reduction after a certain time,but its water capillary absorption was hardly affected by age.When SB dispersion was added,there was no reduction in mechanical strength.The amount of SB added did matter.Addition of 5% SB had a negative effect on most properties compared with RM,except for tensile bond strength.However,the properties of SB-modified mortar(SBMM)were enhanced significantly as the amount of SB was increased from 5% to 20%.Temperature change had different effects on the properties of RM and SBMM.High temperature was beneficial to early flexural and compressive strength development of RM,but caused serious strength reduction at later stages.High temperature enhanced the development of tensile bond strength of RM.Increasing temperature enhanced properties of SBMM,including flexural,compressive,and tensile bond strength.Higher relative humidity improved all measured properties of all mortars.Scanning electron microscope(SEM)observations of the morphology of RM and SBMM at 360 d cured under different conditions accounted well for the changes in mechanical properties.

Influence of Nano-SiO2 Addition on Properties of Sulphoaluminate Cement Based Material

The influences of different nano-SiO2（NS） contents on the mechanical properties and rheological behavior of sulfoaluminate cement（SAC） based composite materials were studied.Results show that with increasing content of NS,the apparent viscosity,and shearing strength of fresh paste gradually increase but the fluidity decreases.With a dosage of 3.0%NS,the tensile and flexural strengths of mortars at 56 days were increased by 87.0%and 84.6%,respectively,compared with that in the absence of NS,indicating that the toughness of hardened mortars is significantly improved.Besides,the exothermic peaks of hydration are obviously increased and will earlier occur,and the second and the third peaks appear 2.61 hours and 2.56 hours earlier,respectively than that in the absence of NS,and the hydration of SAC before 8 hours is accelerated.The forming mechanism of strengths was revealed by scanning electron microscopy（SEM）,hydration heat,X-ray diffraction（XRD） and derivative thermogravimetry（DTG）.The micro-aggregate filling effect and nucleation effect at early age and weak pozzolanic effect at late age of NS make the microstructure more compact,which obviously enhances the strength of SAC mortars.

Influencing factors and optimization on mechanical performance of solid waste-derived rapid repair mortar

There is a great demand for high performance rapid repair mortar(RRM)because of the wide use of cement concrete.Solid-waste-based sulfoaluminate cement(WSAC)is very suitable as a green cementitious material for repair materials because of its characteristics of high early-age strength and short setting time.However,the influence and optimization of various factors of WSAC-based RRM,such as water-to-RRM ratio,binder-to-sand ratio and additives,as well as the further solid waste replacement of aggregate,remain to be studied.This paper comprehensively studied the influence of the above factors on the performance of WSAC-based RRM and obtained a green high-performance RRM by optimizing these factors.The experimental results showed that the early and late strength of the obtained RRM is excellent,and the setting time and fluidity are appropriate,which reflected good mechanical properties and construction performance.Ordinary Portland cement(OPC)doping could not improve RRM strength.It was feasible to prepare RRM with gold tailing sand replacing part of the quartz sand.This paper provides data and a theoretical basis for the preparation of high-performance RRM based on solid waste,expanding the high value utilization of solid waste,which is conducive to the development of a low carbon society.