International Concrete Abstracts Portal

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.

Many mineral admixtures, usually classified as pozzolanic or chemically inert materials, have been used and studied over the years. In order to understand their effects on the compressive strength of cementitious materials, experiments were carried out on mortars including different kinds of fine materials. The aim of this paper, which presents the first part of our work, is to propose an empirical model for the quantification of the physical effects of mineral admixtures, which are responsible for modifications in the compressive strength of mortars for up to 3 months. The quantification is achieved by the separation of the dilution and heterogeneous nucleation effects. The model considers the content (ranging between 0% and 75% of the cement weight) and fineness of the mineral admixtures, and introduces the concept of efficient area, which takes into ac-count the level of probability, varying with filler content, of a fine particle behaving as a nucleation site for cement hydration.

This paper presents a study on the effects of fly ash and calcium nitrite based corrosion inhibitor (CNI) on the compressive strength and corrosion process of steel rein-forcing bars in high-performance concrete. A 34 full factorial design was developed considering water-to-cement ratio, fly ash percent, CNI dosage and cracked condition in a concrete made with silica fume blended cement. Small-scale concrete slabs containing steel reinforcement were cast in concrete with a cover depth of 20 mm. The slabs were subjected to both natural and simulated marine environments with two cycles of wetting and drying per day. Compressive strength of the concrete was determined at 28 days and at one-year. The corrosion activity was monitored on a regular basis using the linear polarization resistance technique. The results show a non-detrimental effect of CNI on corrosion of specimens containing fly ash and silica fume. CNI alone has, in general, no significant effect in decreasing corrosion; however, the crack width strongly affects the corrosion process.

This paper addresses the reaction of alkali activated slags (AAS). First, from literature the most abundant hydration products formed from the hydration of slags are summarized. These products include C-S-H, a hydrotalcite-like phase, a hydrogarnet phase, AFm phases (C4AH13 and CzASHs) and ettringite. Then, two reaction models are established which correlate the mineral composition of the slag (the glass part) with hydration products. Using the proposed models, quantities of hydration products and composition of C-S-H formed can be determined. Finally, the models are applied to four slags selected from literature, and conclusions are drawn.

Supplementary cementitious materials (SCM) such as fly ash, ground granulated blast furnace slag and silica fume are now being extensively used in concrete primarily to enhance mechanical strength and improve resistance to chemical attack, resulting in more durable concrete. Ever since alkali silica reactivity (ASR) was identified in concrete some six decades ago, structure deterioration due to ASR has been extensively documented. Moreover, it has been well established that partial replacement of portland cement by fly ash or slag reduces the expansion due to ASR. Little data are available, however, on the effect of fly ash-slag combinations on ASR resistance. The ASR testing program is an in-house modification of the ASTM C 1260 test. The modifications can be more closely identified with actual field conditions. In this study three different strengths of NaOH test solution (1N, 0.5N, and 0.25N) were used to measure the expansion characteristics of mortar bars made with a reactive aggregate. The other variables included high alkali content cement and a 28-d testing period (in-stead of 14 d). These parameters were then used to evaluate ASR resistance of ternary blends with varying proportions of portland cement, fly ash, and slag. The portland cement replacement was 30%, 50%, and 70%. A set of plain cement mortar bars was also tested in conjunction with the ternary mixes. The results of ASR resistance of fly ash-slag combinations using the modified ASTM C 1260 test are presented.