L. Massidda

Comparison between rheological models for portland cement pastes

Abstract Rheological properties of Portland cement pastes, measured with a rotating viscosimeter, have been correlated by means of different mathematical models. The best results are obtained with Eyrings equation, Herschel & Bulkleys equation and the parabolic equation, while Vom Bergs model only holds for low shears. The authors propose another equation derived from Eyrings but explicitly containing the term τo.

Use of granulated slag from lead and zinc processing in concrete technology

The possibility of using granulated slags resulting from the smelting of lead and zinc in partial, or total replacement of sand in mortars and concretes, has been examined. The major components of these vitreous slags are Ca, Si, Fe and Al compounds with lead concentration of a few percent. They have suitable particle sizes for use as sand and the slag mortars and concretes studied here yielded satisfactory mechanical strengths. The extraction of lead by acid eluants might however create some problems when concretes containing these slags have to be disposed off.

Mechanical properties of epoxy mortars with fly ash as filler

Abstract This paper is concerned with the use of fly ash filler in mortars containing epoxy resins as binders, as a replacement for quartz flour normally employed in such products which find application in pavings for industries, airports and heavily trafficked roads, as well as restoration and protection of concrete works. The stress/displacement curves of bending and compression tests are plotted for the systems tested. The results indicate that the specimens containing fly ash exhibit superior mechanical properties compared with the quartz-filler ones at the shorter curing times, while at longer curing time mechanical performance is comparable.

Low pressure steam curing of compacted lime-pozzolana mixtures

The reaction between Ca(OH)2 and some pozzolanas in compacted mixtures hydrated at low pressure steam curing was investigated. The kinetics of the reaction and the products obtained at 50–90°C were investigated. Some properties of the compacted mixtures, such as porosity, strength and morphological structure were examined. The results obtained show that the pozzolanas examined in this work could be used for the production of materials similar to sand-lime bricks through a low pressure steam curing, instead of the more expensive autoclave treatment.

Dimensional variations, capillary absorption and freeze-thaw resistance of repair mortars admixed with polymers

The results are presented of an investigation aimed at determining the properties required by cement mortars admixed with polymers to be used as overlays in the repair of concrete structures. Tests were conducted using acrylic latex and epoxy resin as polymer admixtures. The adhesion of the modified mortars to different cement bases was tested under stresses induced by dimensional variations (ageing, thermal cycles), capillary absorption and freeze-thaw resistance.

Structure and characteristic of compacts of blastfurnace slag activated by CaSO42H2O

Abstract The hydration of compacts of blastfurnace slag in the presence of gypsum in the range of temperatures between 50°C–180°C was investigated. X-ray difraction, thermal analyses, porosity determinations, compressive strength tests, and scanning electron microscope observations were made. Very strong compacts, expecially by high pressure steam curing, can be obtained. X-ray diffraction analysis evidenced the occurrence of a crystalline phase, identified as plazolite, which fills the initial voids and substantially modifies the porous structure of the compact.

MECHANICAL AND THERMOHYGROMETRIC PROPERTIES OF ADHESION BETWEEN PCMS AND CEMENT SUPPORTS

Abstract A series of cement mortars admixed with either acrylic latex or epoxy resin has been characterized and used for repairing cement supports having different mechanical properties. The performance of the support/repair system under mechanical and thermohygrometric stresses was then assessed. The mortars containing acrylic latex proved particularly effective.

Low temperature steam curing hydration of lime-fly-ash compacts

Abstract Low pressure steam-curing hydration of mixtures with different fly-ash-to-lime ratios compacted at 50 and 150 MPA was studied. The pastes were cured for between 8 and 72 h at 60°, 75° and 90°C. For comparative purposes duplicate samples were treated for 28 days at 25°C. Compressive strength tests were performed on the hydrated samples and the results obtained compared with those pertaining to combined lime and porosity. Higher lime contents of the anhydrous mixtures correspond to greater amounts of reacted product and enhanced strengths. Higher temperature accelerates the reaction rate and produces an increment in strength, even if moderate in passing from 75° to 90°C. This can be attributed to the corresponding increase in porosity of the specimens which contrasts with the positive effect produced by the progression of the pozzolanic reaction.

The use of ‘statbilized earth’ in the conservation of megalithic monuments

The main features of the megalithic monuments in Sardinia, Italy, dated to the Middle-Late Bronze Age, are described. These constructions are in a poor state of preservation, especially those built with stones particularly vulnerable to weathering. To impede water ingress into the masonry structure of these archaeological ruins, it is proposed to use a stabilized earth-based mortar that acts as an effective substrate for a water-repellent polymer.

Crystallization of sodium sulphate in polymer impregnated plasters

Abstract The common occurrence and harmful effects of sodium sulphate make it a major cause of deterioration in plasters. The investigation conducted showed that a plaster composed of eminently hydraulic lime impregnated with water-repellent solutions (a perfluoropolyether or an oligomeric alkylalkoxysiloxane) or admixed with an acrylic latex is significantly more durable than plain plaster. In particular, the different modes of salt crystallization are discussed in relation to the microstructural properties conferred by the polymers, and to the thermohygrometric conditions of the system.