International Concrete Abstracts Portal

Different proportions of fluidized catalytic cracking residue (FOR) and Fly Ash were mixed with cement and their pozzolanic activities were monitored by Thermogravimetric Analysis, as a function of time. Fixed lime contents were calculated to determine the relative pozzolani activities. While FOR reacts with lime at very early ages of hydration, Fly Ash reacts only at longer times. Thermal peaks due to the presence of calcium aluminate hydrate (CAH) and calcium aluminosilicate hydrate (CASH) occurred in many samples.

Over the last few years environmental problems have caught the particular attention of the public, and this has led to various investigations that attempt to study and solve the focal point that cause environmental contamination. The main aim of this study is to determine the presence of polluting elements incorporated into the manufacture of cements and concretes, which might have a noxious effect on health. One way to incorporate this kind of element is by the incorporation of industrial by-products into cement. This paper studies the leaching of trace elements from copper slag, when this by-product is incorporated into cement mortars. A dynamic leaching test has been applied, in which the specimen is studied fully immersed in drinking water. To develop this test has been designed three tanks (reference drinking water, reference mortar and blended mortar), where the samples are continuously flowing. The quantification of leaching elements from the copper slag blended mortar is carried out to different contact time.

The development of self-compacting concrete is considered as a milestone achievement in concrete technology due to several advantages. In order to be self-compactable the fresh concrete must show high fluidity besides good cohesiveness. For the purpose of evaluating these properties, several concrete mixtures were prepared with a water to cement ratio of 0.45 in the presence of an acrylic based superplasticizer at a dosage ranging from 1% to 2% by weight of very fine material fraction (passing the sieve ASTM n° 100 of 150 µm). Either limestone powder or fly ash or recycled aggregate powder (that is a powder obtained from the rubble recycling process) were used as mineral addition, in order to assure adequate rheological properties, in terms of cohesiveness, in the self-compacting concretes. Preliminary rheological tests were carried out on cement pastes containing these mineral additions. In some cases, recycled instead of natural aggregate was used by subtituting either the coarse or the fine aggregate fraction. The fresh concrete properties were evaluated through the slump flow, the L-box test and segregation resistance. Compressive strength was measured on hardened concretes at 1, 3, 7 and 28 days of wet curing.

Studies on the viability of high calcium fly ash from coal combustion are being conducted in our laboratory to produce a new kind of low-energy cement. The process presents important environmental advantages, such as a reduction of CO2 emission compared to that produced by the conventional technology of portland cement manufacture. Furthermore, the processing temperature is also considerably reduced. The low-energy cement shows potential for good hydraulic activity for application in construction. The changes of fly ash composition were followed by X-Ray Diffraction (XRD), FT Infrared (FTIR) spectroscopy and BET surface area analysis.

Four of the most widespread sedimentary zeolitic tuffs were tested to evaluate their pozzolanic character. The zeolitic tuffs were: a chabazite-phillipsite-rich tuff from Tufino (Naples, Italy), a phillipsite-rich tuff from Marano (Naples, Italy), a clinoptilolite-rich tuff from Eskisehir (Anatolia, Turkey) and an erionite-rich tuff from Agua Prieta (Sonora, Mexico). Suitable tuff-lime mixtures were cured at room temperature and the reactivity data were collected in form of kinetic curves. All the tuffs showed a pozzolanic activity better than that reported for a typical pozzolan from Campi Flegrei (Naples), i.e., the volcanic glassy material precursor of the Neapolitan tuffs. Tuff reactivity was tentatively related to the microporosity of the zeolite components of the single tuffaceous materials. Zeolitic materials were also evaluated, investigating the behavior of blended cements prepared by mixing portland clinker, tuffs and gypsum. The pozzolanic behavior of the blended cements was estimated according to the European Standards, using the so-called Fratini's test, that allows to evaluate whether the material under investigation, regardless of its nature and the mixture ratio, is able to combine with Ca(OH)2 produced by hydration of portland clinker. Although this test was positive for most prepared blends, X-ray diffraction analysis demonstrated that the hardened pastes still contained residual amounts of Ca(OH)2 confined in the inner part of the manufacts.