Hydration Products of Cement-silica Fume-quartz Powder Mixture under Different Curing Regimes

Composition, morphology, and structure of hydration products in hardened pastes of three kinds of blended cement（cement-silica fume, cement-quartz powder and cement-silica fume-quartz powder） hydrated under different curing regimes（standard curing, 90 ℃ steam curing, 200 ℃ and 250 ℃ autoclave curing） were investigated by X-ray diffraction and field emission scanning electron microscope equipped with EDAX system. Results showed that the main hydration products in three kinds of hardened pastes under standard curing condition are all C-S-H gels, CH, and AFt. Under 90 ℃ steam curing condition, the main hydration products of cement-silica fume and cement-silica fume-quartz powder are C-S-H gels, whereas those of cement-quartz powder are C-S-H and CH. Under 200 or 250 ℃ autoclave curing condition, no obvious crystallized CH phase is found in hardened pastes of three kinds of blended cement, and C-S-H gels are transformed into one or more crystalline phases such as tobermorite, jennite, and xonotlite. The chemical composition and morphology of these crystalline phases depend on the composition of mixture and autoclave temperature.

Investigation of the Interfacial Transition Zone between Aggregate-Cement Paste by AC Impedance Spectroscopy

Three different types and sizes of coarse aggregate were chosen,and the alternating current（AC） impedance of cement paste samples with and without aggregate was measured at different curing ages.Based on Song’s equivalent circuit model,the electrical properties from the AC impedance results were obtained,and the resistance of connected pores RCCP was used to characterize the microstructure of the interfacial transition zone（ITZ）.The results show that the RCCP of concrete sample with aggregate is lower than that of cement paste sample,which indicates that the introduction of aggregate in cement paste makes the ITZ porous.Furthermore,for the same type of aggregate,an increase in particle size leads to a more porous ITZ,which accounts for the “water effect” and a larger aggregate would accumulate a thicker water film around it.In addition,for the same size of aggregate,the physical interaction between aggregate and cement paste is dominant in early age,and the microstructure of the ITZ around limestone aggregate is denser,which mainly depends on its rough surface and high water absorption.However,the microstructures of the ITZ around granite and basalt aggregates are denser in later age,which may be due to their higher chemical activity,and the chemical interaction between them and cement paste resulting in the generation of more hydrates.AC impedance spectroscopy thus proves to be powerful for evaluation of the microstructure of the ITZ.

Utilization of Red Mud as Raw Material in the Production of Field Road Cement

The total utilization amount of red mud is limited due to its high content of alkali,heavy metals and naturally occurring radioactive element.In order to rationalize the use of red mud,a typical field road cement using dealkalized red mud（content of alkali lower than 1%） as raw material was firstly prepared in this paper.Then,a preliminary research on the radioactivity of the red mud based field road cement has been carried out.For that reason,two samples of raw materials were prepared.One was with ordinary raw materials,as the control group（CG）,the other was with 23 w % red mud,as the experimental group（EG）.The clinkers were acquired by sintering the above two raw materials at 1 400 ℃.Subsequently,the two types of cement prepared by the above two kinds of clinkers were tested by measuring the normal consistency,setting time,mechanical strength and drying shrinkage.Meanwhile,the hydration products of the two types of cement were examined by XRD analysis at the curing age of 6 hours,1,3,7,and 28 days,respectively.The radioactivity of the two kinds of cement clinkers was then measured by gamma-ray spectrometry.The experimental results indicate that the main mineralogical phases components in the EG field road cement clinkers are C3S,C2S,and C4AF,the 28 days flexural and compressive strength of the EG field road cement mortars could be up to 8.45 and 53.2 MPa,respectively.The radioactive measuring results of the EG field road cement show that the value of radium equivalent activity index（Raeq） is 254.8 Bq/Kg-1,which is lower than the upper limit.