International Concrete Abstracts Portal

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.

An estimated 144 metric tons of mercury are emitted into the atmosphere of the continental United States each year, and approximately one-third of these emissions come from coal-fired utility boilers. Maximum achievable control technology (MALT) for mercury, effective in 2007, may significantly impact coal combustion byproduct reuse initiatives, especially the utilization of fly ash in concrete. If powdered activation carbon (PAC) injection is selected as a mercury control strategy, both the percent of car-bon in fly ash and the mercury content in the coal combustion byproduct will increase. This paper describes an EPRI funded project to investigate the possible release of mercury during curing of concrete containing fly ash and mercury-loaded PAC, and to determine if conditions exist during concrete curing that may result in the release of mercury from the coal combustion byproducts in the concrete matrix. EPRI initiated this research program to address issues associated with mercury contaminated fly ash that could evolve from installation of MACT technology for mercury control.

Four rectangular concrete monoliths, each 2.5x4.Ox5.0-m high, were cast in Laval, Quebec in 1989. TWo control monoliths No. 1 and 2 were cast with concrete made with AST M Type I cement and with a modified version of ASTM Type 11 cement, respectively. Test monoliths No. 3 and 4 were cast using superplasticized high-volume fly ash concrete incorporating 56% fly ash as replacement for cement and high-volume slag concrete incorporating 60% granulated blast furnace slag as cement replacement. All monoliths were instrumented with thermocouples to monitor temperature rise. A large number of specimens were cast from concrete for each monolith for testing compressive, flexural, and splitting-tensile strengths, drying shrinkage, Young's modulus of elasticity, freezing and thawing and de-icing salt scaling resistance. The results show that the adequate strength development and low temperature rise characteristics of high-volume fly ash concrete, combined with the ability to place the concrete in one 5-m continuous lift, make this type of material very attractive for mass concrete applications. On the other hand, the significant high temperature rise and high later-age strength of high-volume slag concrete make this type of concrete more attractive for structural applications but not for mass concrete applications.

An investigation of the activation of Class C and Class F fly ash as well as granulated blast furnace slag has established that the amount and nature of the calcium containing phases in these materials significantly affect the activation mechanism. The majority of calcium in blast furnace slag is associated with either Si or with S and it can be activated either by use of a highly alkaline solution or by an alkaline solution containing soluble silicate to produce a solid material having sufficient mechanical strength. Class C fly ash contains calcium that is partly structured with aluminium and silicon and it has been found that this class of fly ash can only be activated using a highly alkaline solution containing soluble silicate. It has been observed that Class F fly ash cannot be successfully activated by either a highly alkaline solution or an alkaline soluble silicate solution, but by a very highly alkaline soluble silicate solution. It is proposed that the poor activation of Class F fly ash is due to this material having significantly lower calcium content than either blast furnace slag or Class C fly ash and that the calcium is in an isolated form.