Javed I. Bhatty

Compressive Strength of Municipal Sludge Ash Mortars

Sludge ashes produced by the incineration of municipal sewage wastes are becoming increasingly difficult to dispose of in landfills, and there is a resulting increase of interest in disposal by inorporation in building materials. In the present study, a comprehensive test program was developed to examine the potential for using the ash as a fine aggregate in mortar. The strength characteristics of mortars prepared from sludge ash with addition of fly ashes (both Classes C and F) and varying amounts of cement and lime were cured under standard laboratory conditions for periods of 1, 3, 7, 14, and 28 days before testing for compressive strength. The results indicate that the addition of sludge ash adversely affects the strength behavior of mortars. Although partial substitution of sludge ash with fly ash gave improved results, strengths were always less than those obtained from control mortars using sand. Addition of fly ashes also improves mortar workability. The addition of lime in place of cement reduces strength.

A review of the application of thermal analysis to cement-admixture systems

Abstract The application of thermal analysis in the investigation of the role of chemical admixtures in cement hydration is reviewed. The relevant literature published on DTA, TG and DTG techniques during the past two decades has covered both the kinetic and mechanism aspects of cement hydration, with or without the presence of accelerators, retarders/water reducers and plasticizers. Two vital components of cement, namely C 3 S and C 3 A, have been of particular interest to researchers, C 3 S being the major compound controlling the overall hydration, and C 3 A being the most reactive component controlling the initial setting of the cement. Modifications of various products that develop in cement pastes in the presence of admixtures as monitored by thermal analysis are quoted frequently in this review in order to elucidate the mechanism of the action of admixtures on the cement hydration.

Moderate strength concrete from lightweight sludge ash aggregates

Abstract A range of artificial aggregates has been developed from incinerated municipal sludge ash and tested in concrete. The ash is either pelletised or slabbed, and subsequently fired until it sinters and expands to form lightweight products. From the tests conducted on size, grading, bulk density, absorption and compressive strength, it appears that both the pellets and slabs have potential as lightweight aggregates. Their use in producing moderate strength concrete of up to 2000 psi and unit weight 50 lb/cu ft (800 kg/m3) via steam curing has specifically been investigated. Although concrete prepared from the pellet form of aggregates are somewhat heavier, they exhibit superior strength than those prepared from the slabs and commercial aggregates derived from expanded clays. It is anticipated that because of their spherical shape and uniform size distribution, the pellets could provide better workability and compaction; and their lower moisture absorption may also render them as potentially better thermal insulators.

Lightweight aggregates from incinerated sludge ash

A range of artificial aggregates has been developed from incinerated sewage sludge ash. The ash is either pelletized or slabbed and subsequently fired until it sinters and expands to form lightweight products which are later graded for use as aggregates in concrete. From the standard tests conducted on size grading, bulk density, absorption and fracture strength, it appears that both the pellets and slabs are potentially suitable as lightweight aggregates in concrete. Preliminary studies on concrete incorporating these aggregates support this hypothesis. No studies of potential containment release at high temperature was made during these studies.

Use of thermal analysis in the hydration studies of a type 1 portland cement produced from mineral tailings

Abstract A high-strength Type 1 cement produced from raw taconite and copper-nickel tailings of Minnesota is the subject of hydration studies by using thermal methods such as TGA and DTA. Hydration is measured in terms of hydration product formation and the amount of bound water and free calcium hydroxide incorporated in them. When cured under identical conditions, the Type 1 “tailing” cement, compared to an ordinary Type 1 Portland cement, exhibits better hydration properties. This is attributed to its higher tricalcium silicate content, a component that hydrates faster and also contributes much to the strength development. Correlation between the degree of hydration and strength is suggested and a simple mathematical expression relating these parameters proposed.

Estimation of calcium hydroxide in OPC, OPC/PFA and OPC/PFA/polymer modified systems

Abstract Formation of calcium hydroxide in a hydrating ordinary Portland cement (OPC) not only determines the process of cement hydration but also influences the ultimate mechanical properties. Calcium hydroxide is a well crystallized material and possesses a typical morphology which can change upon the incorporation of any additives and admixtures capable of altering the hydration mechanisms in a given cement paste, thus resulting into varying degrees of calcium hydroxide formations. The additives used in the present work are the pulverized fuel ash (PFA) and a Versicol W13 polymer. Thermogravimetric (TG) and differential thermal analysis (DTA) techniques have been used to estimate the quantity of calcium hydroxide present in the hydrating OPC, OPC/PFA and OPC/PFA polymer systems. The results have shown that by incorporating PFA and W13 polymer into OPC the quantity of calcium hydroxide formed is reduced apparently due to a secondary reaction taking place between calcium hydroxide and silica present in PFA.

PORTLAND CEMENT PRODUCTION USING MINERAL WASTES

A Type I Portland cement has been produced using anorthite from copper-nickel tailings and raw taconite tailings. The cement exhibited better strength properties than ordinary Type I Portland cement and gave a stronger concrete when tested under identical curing conditions. Factors leading to the attainment of these higher strength values are identified and their effects on the ultimate mechanical properties of cement are discussed. It is also anticipated that the compositional variety of tailings may also have other beneficial effects on long-term cement behavior such as resistance to sulfate attack.

Hydration versus strength in a Portland cement developed from domestic mineral wastes ― a comparative study

Abstract Early age hydration studies on fresh pastes of a Type I cement produced from local mineral tailings have been conducted by using thermal techniques such as DTA and TGA and degrees of hydration at varying time intervals have been estimated in terms of nonevaporable water and free calcium hydroxide incorporated in the hydration products. The results are subjected to an earlier proposed expression which gives a direct correlation between strength and degree of hydration for a given hydrating cement paste except for the period of low reactivity, commonly referred to as the dormant period exhibiting very low heat evolution in a calorimetric plot, when cement remains plastic while still undergoing a certain degree of hydration. It is noticed that the critical degree of hydration at which strength starts developing is a function of hydration time and theoretically corresponds to the termination of the acceleration period when tricalcium silicates and dicalcium silicates in the cement have hydrated to produce enough hydration products to intermesh and initiate early strength. The experimental data are compared with those of a commercially available Type I cement and are interpreted in terms of strength development as a function of hydration.

The derivation of kinetic parameters in analysis of portland cement for portlandite and carbonate by thermogravimetry

The analysis of hydrated portland cement can be facilitated by the use of thermal analysis techniques. This is especially true with regard to the estimation of the portlandite phase (calcium hydroxide [Ca(OH) 2 ]) which isone of the major phases in set portland cements. There are various references in the literature to the use of thermogravimetric analysis (TG) for the estimation of free Ca(OH) 2 . Papers by Midgley and Ramachandran have shown it to be reliable. It has been used by Dollimore et al. to estimate the Ca(OH) 2 in portland cement (OPC), OPC/pulverized fly ash (PFA), and OPC/PFA/polymer pastes. It is also shown here that the method can be adapted to indicate the relative crystallinity of the Ca(OH) 2 present. Taking the investigation into a higher temperature region on the thermal analysis equipment also means that an estimate of the calcium carbonate can also be made. This is important in aged mortars. The method can be extended to cover the quantitative analysis of calcium sulfate if present.

Aspects of the Chemistry of Poly (Ethylene Terephthalate). IV. Hydrolysis of Poly(Ethylene Terephthalate) in the Melt Phase

Abstract The effect of water vapor pressure on the molecular weight of molten poly (ethylene terephthalate) has been followed by measurement of the changes which occur in the intrinsic viscosity and the end-group concentrations upon hydrolysis. It was found that phosphoric acid is highly effective as a stabilizer; the hydrolysis rate constant (Kh) decreasing from 7.6 × 10−7 mol−1s−1 for nonstabilized to 2.5 × 10−7 mol−1s−1 for the stabilized polyester at 290°C and water vapor pressure of 20 mmHg.