Utilisation of limestone powder in self-levelling binders

The rheology of a suspension is always a function of "Fluid Phase Rheology". The rheology of concrete can therefore never be optimal if the rheology of the concrete fluid phase (cement-water-additive) is not optimal. To reach the optimum mix design for Self-Compacting Concrete, it is important to find out the right combination of cement and filler material, both amount and type. The replacement of cement by mineral additives strongly influences the flow resistance; it may improve or worsen the workability. The successful utilization of quarry dust in self-levelling cement pastes could turn this waste material into a valuable resource. The effect of cement replacements with three types of limestone powders produced from different quarries on the rheology of the fresh paste has been studied in this research. Also the mechanical and drying shrinkage properties of paste in the hardened state has been investigated. A 10 percent replacement of cement with a special type of quarry dust was found to lead the best performance at fresh state rheological properties and at hardened state compressive strengths. All filler additions decreased the drying shrinkage of cement pastes at different orders when compared with pure cement paste specimens. The positive effects of quarry dust on fresh and hardened properties of self-levelling binders make this material a feasible additive besides its economical and environmental advantages

The effect of cement alkali content on ASR susceptibility of mortars incorporating admixtures

In this study, the effects of three types of plasticizing chemical admixtures (modified lignosulfonate, sulfonated naphthalene formaldehyde and polycarboxylate based) on deleterious expansion due to alkali-silica reaction (ASR) have been investigated. Two different types of cements with low (0.53 Na2O eq.) and high (0.98 Na2O eq.) alkali contents, a non-reactive crushed limestone as fine aggregate and a reactive river sand were used within the scope of the experimental program. ASR tests were conducted according to accelerated mortar bar method (ASTM C 1260). Additionally the flow value, dry unit weight, capillary water absorption and compressive strength tests were performed. Test results indicated that mortars prepared with inert fine aggregate caused no significant expansion, regardless of cement type, admixture type and dosage. However, for mixes containing reactive sand, admixtures increased or decreased the expansion values (compared to plain mortars) depending on the alkali content of cement used. The magnitude of change of expansion also depended on the type and amount of admixture incorporation which have a dominant effect on stability and compactability of mortars. The high-alkali cement usually revealed the ASR expansion augmentation behaviour of admixtures. In contrast, low alkali cement decreased the expansion values compared to the control specimens. (c) 2006 Elsevier Ltd. All rights reserved

Effect of cement C3A content on properties of cementitious systems containing high-range water-reducing admixture

The effect of cement tricalcium aluminate (C3A) content on the properties of cement paste, mortar, and concrete mixtures containing high-range water-reducing (HRWR) admixture was investigated. Three commercial Type I cements prepared with the same raw material and same gypsum rock interground with clinker, but with different C3A contents (by changing mixture proportions), were used. The fresh state, rheological properties, and compressive strength of the mixtures were studied. Moreover, X-ray diffraction (XRD) patterns of 6-h-age paste mixtures from each cement were obtained. By reducing the C3A content of the cements, the fresh state, rheological, and consistency retention properties of the mixtures improved; however, the strength of the mixtures at early ages decreased. The difference between strength of the mixtures closed at later ages. The XRD analysis of the pastes revealed the formation of more ettringite in the paste prepared from high C3A content cement. © 2017 American Society of Civil Engineers

Relationship between clinker porosity and interstitial phase morphology

The results of interstitial phase morphology variations of two clinkers with respect to their porosity differences are presented in this paper. Single clinker nodules with an average diameter of 10-15 mm were used in the analyses. Porosity ratios and phase compositions were determined on scanning electron microscope images of polished clinker surfaces by using image processing techniques and, in addition, morphological characterisation of interstitial phases was realised. The results showed that the porosity distribution of a single clinker nodule is heterogeneous and a relationship exists between the average interstitial phase thickness and porosity. A dendritic interstitial phase morphology is associated with porous clinker structure. The porosity ratio depends on the degree of dendritic structure formation. Dendritic structures form because local heat transfer conditions produce an undercooled liquid, which produces an unstable liquid-solid interface and crystallites which propagate in front of such an interface become surrounded by a liquid showing an increasing degree of undercooling. As crystalline solids typically occupy space more efficiently than their liquids, the solidification of the interdendritic regions then produces porosity at that stage of cooling. The morphological variations in interstitial phases and porosity may cause differences in the performance of cements produced from these clinkers