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.

The need to attain the correct assessment of industrial by-products and wastes re-quires an in-depth knowledge of their characteristics. One of the most important characteristics that affects in the aptitude of a thermally calcined product is the calcining conditions like temperature and stay in furnace. This is the aim of the current work which considers the importance of calcining conditions on the pozzolanic properties of a paper sludge as cementing material. The by-product used for this research is a Spanish paper sludge coming from a paper industry which uses 100% of recycled paper as raw materials. Due to the high content of organic material and calcium carbonate and, to the presence of different clayey minerals in sludge like kaolinite and talc, the calcining conditions play an important role on the mineralogy and pozzolanic activity of this sludge. For this reason, different intervals of temperature between 700 and 800°C and, different times of stay in furnace (2.5 and 5h) are studied in order to get the best pozzolanic properties for the paper sludge. The reaction kinetics of pozzolanic reaction cured at 40°C varied with the calcining conditions. The main crystalline phases identified by XRD were hydrocalumite (Ca4Al2O6C121OH2O) and calcium aluminium carbonate hydrate (Ca4Al2O6CO311H2O), stratlingite and hydrogamet.

The rate of chloride ingress in concrete not only depends on the intrinsic proper-ties of concrete but also on the magnitude of applied stresses and the nature of micro-crack propagation under these stresses. Limited information is available on the influence of these factors on the chloride ion penetration into concrete. The significance of applied stresses and the corresponding microcracking behaviour on the transport properties of concrete could provide useful information on the service life prediction of the concrete structure. To date, studies on the chloride ion transport into concrete are primarily based on concrete specimens that are not subjected to any stresses, particularly under sustained uniaxial compression. In the present study, the characteristics of microcracking and chloride diffusion into Grade 20 and 40 concretes are being investigated jointly by UNSW and CSIRO. The concrete specimens were loaded uniaxially in compression and sustained for a maximum duration of 18 months. Chloride ion penetration and micro-crack evaluation of these specimens were monitored periodically. This paper presents some early results on the apparent chloride diffusion coefficient obtained from Grade 20 and 40 concrete specimens that have been subjected simultaneously to sustained compressive stresses and 3% NaCl solution immersion for 90 days. Three levels of sustained compressive stresses at 20%, 35% and 50% of the ultimate strength were investigated. In addition, microcrack evaluation of the companion specimens (subjected to the same stress levels for 90 days) was also carried out. Microscopy technique was used to deter-mine the bond crack length in the concrete after the 90-day sustained period. At 35% sustained stress level, microcracks appear to be stable. However, the apparent chloride diffusion coefficient (Da) was found to decrease when compared with the unloaded control specimen. At 50% sustained stress level, a further reduction in D. was observed even though microcracks appear to have propagated.