Caijun Shi

Acid corrosion resistance of different cementing materials

Abstract This study has investigated the corrosion of different hardened cementing materials, such as Portland cement (PC), alkali-activated blast furnace slag cement (ASC), lime–fly ash (LFA) blend and high alumina cement with gypsum and lime (HAC), in pH 3 nitric acid, pH 3 acetic acid, and pH 5 acetic acid solutions. Experimental results indicated that PC pastes were corroded faster than ASC and LFA pastes, and pastes consisting of HAC were quickly dissolved in these acid solutions. PC pastes are more porous than ASC pastes but much less porous than LFA pastes. Thus, the corrosion of hardened cementing materials in acid solutions depends on the nature of the hydration products rather than the porosity of the hardened cementing materials: calcium silicate hydrate (C-S-H) with a low C/S ratio is the main hydration product in ASC and LFA pastes, while C-S-H with a high C/S ratio and Ca(OH)2 are the main hydration products in hardened PC pastes. Ca(OH)2 decomposes as the pH drops below 12, and C-S-H decalcifies as the pH decreases, and decomposes for pH values below 9. The mixture of high alumina cement, gypsum, and lime results in the formation of an ettringite-based matrix, which was dissolved very quickly in these acid solutions.

Effect of Supplementary Cementing Materials on the Specific Conductivity of Pore Solution and Its Implications on the Rapid Chloride Permeability Test (AASHTO T277 and ASTM C1202) Results

The American Association of States Highway and Transportation Officials (AASHTO) Test Method T277--Rapid Determination of the Chloride Permeability of Concrete and the American Society of Testing and Materials (ASTM) C1202--Electrical Indication of Concretes Ability to Resist Chloride Ion Penetration have specified a rapid test method to rank the chloride penetration resistance of various concretes by applying a potential of 60 V DC to a concrete specimen and measuring the charge passed through the specimen during 6 hours of testing. The method is essentially a measurement of electrical conductivity of concrete, which depends on both the pore structure and the chemistry of the pore solution. Analyses based on published results have indicated that the replacement of portland cement with supplementary cementing materials, such as silica fume, can reduce the electrical conductivity of concrete more than 90% because of the change in pore solution composition in the concrete. Chemical composition of pore solution has little to do with the transport of chloride ions in the concrete; thus, it is not correct to use passed charge to rank the chloride penetration resistance of concrete made with supplementary cementing materials.

Response of Various Solidification Systems to Acid Addition

Abstract Experiments were conducted to examine the responses of five different solidification systems, with and without waste, to acid addition. The chosen cementing systems were: portland cement, portland cement with silica fume, alkali-activated blast furnace slag, lime and coal fly ash, and high alumina cement with lime and gypsum. The solidified products were tested at several ages using the Acid Neutralisation Capacity test, a series of batch extractions of ground wastes with varying amounts of nitric acid, which allows a titration curve to be plotted. Experimental results indicate that different cementitious systems vary in their response to acid addition; the location of the pH plateau of the titration curve depends on the nature of the hydration products formed by the binder system and is affected by waste components.

Variability of field solidified waste

The properties of solidified waste prepared in the field can be anticipated to be more variable than those of solidified samples prepared in the laboratory, because of the greater difficulty in controlling parameters such as untreated waste and binder homogeneity, accuracy of dosage, mixing efficiency, changes in handling characteristics caused by scale-up, etc. However, there is little information available regarding the effect of field variability on solidified waste properties. In a field trial conducted by the Wastewater Technology Centre it was found that the proportions of the waste (electric arc furnace dust) and binder (activated blast furnace slag) could be controlled within 2%, expressed as a fraction of the mix. Comparison of comprehensive physical and chemical test results for laboratory and field solidified specimens of electric arc furnace dust showed that the physical properties of the field solidified material were sensitive to changes in water addition. Chemical properties and leachability were most affected by changes in pH and acid neutralization capacity. However, both physical and chemical properties remained within the desired range.

An examination of interference in waste solidification through measurement of heat signature

Abstract The hydration of cementing materials is accompanied by heat evolution which is closely related to their structure development. The presence of wastes usually interferes with the hydration of cementing materials. This study examined their interference in waste stabilization/solidification processes through the measurement of adiabatic heat evolution using a computerized Quadrel™ system. Two cementitious materials, an alkali-activated blast furnace slag binder and an ASTM Type I portland cement were used to solidify an electric arc furnace (EAF) dust, which has high concentrations of B, Cr, Hg, Pb, Ni and Zn. The EAF dust contents were 0, 30 and 60% by mass. Different mixing conditions were also examined. The interference of EAF dust with the hydration of cementing materials was described using several parameters derived from the heat evolution curves: equivalent initial time of setting (equivalent time at 20°C); total heat evolution at initial time of setting; equivalent final time of setting, total heat evolution at final time of setting and total heat evolution at equivalent time of 28 and 90 days. Experimental results indicated that the Quarel™ system was a useful tool to examine the interference in waste stabilization/solidification and to assist with the selection of cementing materials.

Conversion of a waste mud into a pozzolanic material

Abstract This work investigated the conversion of a waste mud from alum production into a pozzolanic material. X-ray diffraction analysis indicated that the main components in the mud were kaolinite (Al 2 O 3 .2SiO 2 .2H 2 O), quartz (SiO 2 ) and titanium oxide (TiO 2 ). After calcination at 750 o C for 5 h, kaolinite in the mud converted into metakaolinite (Al 2 O 3 .2SiO 2 ), and quartz and titanium oxide remained unchanged. The calcined mud showed very high pozzolanic reactivity. The addition of chemical activators such as Na 2 SO 4 and CaCl 2 accelerated the pozzolanic reaction between lime and calcined mud and increased the strength of lime–calcined mud very significantly.

Acid Resistance of Different Monolithic Binders and Solidified Wastes

Abstract Laboratory tests which add acid to a ground solidified product are useful for examining acid neutralizing capacity and dissolution of metals as a function of pH, but do not examine the effect of acid on the monolithic structure of the cement-based matrix, which is also important for reducing leachability of contaminants. In this study, specimens of five different cementing systems (portland cement, portland cement with silica fume, alkali-activated ground blast furnace slag, coal fly ash with lime, and high alumina cement with lime and gypsum), with and without waste addition, were immersed in three types of acid (pH 3 nitric acid, pH 3 acetic acid and pH 5 acetic acid) to investigate the effects of acid attack on a monolithic matrix. It was found that calcium silicate hydrate-based formulations with a low Ca/Si ratio have the greatest acid resistance. Acid resistance of sulphated high alumina cement specimens was poor.

Field validation of test methods for solidified waste evaluation - A status report

Application of solidification/stabilization as a treatment technology for hazardous wastes has been hindered by the lack of a regulatory approval mechanism for solidified wastes. The Wastewater Technology Centre (WTC) has developed a protocol for evaluation of solidified wastes, which uses the performance of a solidified product in twelve laboratory test methods to recommend one of four categories of utilization and disposal. In order to facilitate acceptance of the protocol, a validation study of the test methods has been initiated by the WTC. A 63 m{sup 3} field test cell has been constructed using electric arc furnace dust solidified with an activated blast furnace slag binder system. The behavior of the solidified waste in the field will be investigated by monitoring of leachate and testing of core samples, and compared with properties measured in the laboratory.

Quality analysis/quality control tests for field stabilization/solidification—2. Untreated waste, sodium silicate solution and solidified waste

This paper reports on the efficacy of selected quality analysis/quality control testing procedures that were used during a full-scale stabilization/solidification trial of an arc furnace dust with high multiple contaminants. The quality analysis/quality control test results of untreated waste, sodium silicate solution and solidified waste are discussed. Moisture content of the untreated waste was measured to control water addition. It was found that sodium silicate concentration in solution was linearly related to its specific gravity. Thus, hydrometer measurement of specific gravity was used to control the silicate concentration in solution. Bulk density, moisture content, and cone and K-slump of freshly solidified wastes were measured. Laboratory measurement of bulk density and moisture content of freshly solidified wastes correlated well with water addition. It appeared from the field data that bulk density measurement underestimated the actual water-to-solid ratios, while moisture content measurement overestimated them. Cone slump and K-slump measurements fluctuated widely, the measurements were within the range normally observed from different types of concrete.