Methods for Improving Volume Stability of Steel Slag as Fine Aggregate

Suitable methods for enhancing the volume stability of steel slag utilized as fine aggregate were determined. The effects of steam treatment at 100 ℃ and autoclave treatment under 2.0 MPa on the soundness of steel slag sand were investigated by means of powder ratio, linear expansion, compressive and flexural strength. DTA, EDX, XRD and ethylene glycol methods were employed to analyze both the treated slags and susceptible expansion grains. Experimental results indicate that powder ratio, content of free lime and rate of linear expansion can express the improvement in volume stability of different treated methods. Steam treatment process cannot ultimately prevent specimens from cracking and decrease of strength, but mortar made from autoclave treated slag keeps integration subjected to hot water of 80℃ until 28 d and its strength do not show significant decrement. The hydration of over-burn free lime and periclase phase are the main cause for the disintegration or crack of untreated and steam treated steel slag＇s specimens. Autoclave treatment process is more effective than steam treatment process on enhancement of volume stability of steel slag.

Shrinkage and Expansive Strain of Concrete with Fly Ash and Expansive Agent

The effects of fly ash and MgO-type expansive agent on the shrinkage and expan-sive strain of concrete with high magnesia cement were investigated. The results show that high volumes of fly ash may reduce the shrinkage strain of concrete and inhibit the expansive strain of concrete with MgO-type expansive agent, but can not eliminate the shrinkage of concrete. MgO-type expansive agent may produce expansive strain and compensate the shrinkage strain of concrete, re-lieve the cracking risk, but the hydration product of magnesia tends to get together in paste and pro-duce expansive cracking of concrete with high magnesia content according to SEM observation.

Magnesia Modification of Alkali-Activated Slag Fly Ash Cement

A new type of magnesia modification alkali-activated cement was prepared, the strength, setting time, shrinkage ratio and cracking behavior, as well as the composition and structure of the hydration product were investigated. The results indicate that the setting time of this cement is similar to that of the ordinary commercial cements; its strength reaches the standard of 42.5 degree cement, its cracking resistance has been remarkably improved because of the micro-aggregate effect of fly ash and shrinkage compensating of magnesia.

The Improvement Effects of NaH_(2)PO_(4) and KH_(2)PO_(4) on the Properties of Magnesium Oxysulfate Cement

Sodium dihydrogen phosphate (NaH_(2)PO_(4)) and potassium dihydrogen phosphate (KH_(2)PO_(4)) were selected as additives for magnesium oxysulfate (MOS) cement.The phase composition and the microstructure of MOS cement were characterized using X-ray diffraction (XRD),thermogravimetric analysis (TG-DSC),Flourier transform infrared spectroscopy (FT-IR),mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM).It is found that both NaH_(2)PO_(4) and KH_(2)PO_(4) lead to an increase in the compressive strength and an improvement in the volume stability of MOS cement.The XRD,MIP and SEM results show that the addition of NaH_(2)PO_(4) or KH_(2)PO_(4) does not change the phase composition of MOS cement but promotes the formation of strength phase of 5Mg(OH)_(2)·MgSO_(4)·7H_(2)O (5·1·7 phase).This phase brings a considerable improvement in the microstructure of MOS cement,which has a positive effect on the properties of MOS cement.

Effects of the Lithologic Character of Manufactured Sand on Properties of Concrete

Six representative parent rocks of sand, including limestone, quartzite, gneisses, granite, Basalt and Marble were selected to conduct a systematical research on the effects of various lithologies of manufactured sand on the workability, mechanism properties, volume stability and durability of manufacturedsand concrete. The experimental results show that the strength of manufactured-sand concrete is slightly higher than that of natural-sand concrete. Furthermore, substituting 15% cement of the concrete mixture with equal quantity of the six different lithology stone powder respectively, the data indicated that they can improve the concrete’s workability, postpone the plastic cracking time, enhance the anti-cracking grade, and have no obvious effect on the properties of antifreeze and sulfate attack resistance but reduce the capability to resist chloride ion penetration. Moreover, the differences in concrete’s workability, mechanism properties, volume stability and durability caused by various lithologies of manufactured sand and stone powder were not significant and the influence of lithology variety on the macro properties of concrete could be neglected eventually.

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 Treated Graphite on Properties of Al_2O_3-SiC-C Castables

Al2O3 - SiC - C castables with 2% pitch or 2%, 4% and 6% treated graphite, respectively, were prepared based on the basic formulation of traditional Al2O3 - SiC - C castables. The flowability of castables, and bulk density, volume stability, strength, oxidation resistance and slag resistance of specimens fired at 110 ℃, 1 100 ℃, and 1 500 9Z respectively were comparatively studied. The results showed that： （1） With carbon source changing from pitch to treated graphite and the increase of treated graphite addition, water addition of castables increased, bulk density of specimens fired at different temperatures increased firstly and then decreased, strength after drying decreased obviously, strength after firing and oxidation resistance changed slightly, hot modulus of rupture increased obviously; （2） Slag resistance of specimen with treated graphite was worse than that of specimen with the same amount of pitch, but the former was obviously improved with the increase of treated graphite addition.