Influence of volcanic originated natural materials as additives on the setting time and some mechanical properties of concrete

Monitoring the setting process of mortars by ultrasonic P and S-wave transmission velocity measurement

Mineral trioxide aggregate with anti-washout gel - properties and microstructure.

The objective of this paper was to evaluate the physicochemical properties of calcium silicate cements with different chemical compositions, associated with radiopacifying agents. Mineral trioxide aggregate (MTA) Angelus, calcium silicate cement with additives (CSC), and resinous calcium silicate cement (CSCR) were evaluated, with the addition of the following radiopacifiers: microparticles (micro) or nanoparticles (nano) of zirconium oxide (ZrO2), niobium oxide (Nb2O5), bismuth oxide (Bi2O3), or calcium tungstate (CaWO4). Setting time was evaluated using Gilmore needles. Solubility was determined after immersion in water. The pH and calcium ion release were analyzed after 3, 12, and 24 h and 7, 14, and 21 days. The data obtained were submitted to analysis of variance and Tukey’s test, at a level of significance of 5 %. CSC + CaWO4 and CSCR + ZrO2 micro, Nb2O5 and CaWO4 presented results similar to MTA, with a shorter final setting time than the other associations. CSC and CSCR+ ZrO2 micro presented a higher degree of flow. All the cements evaluated presented low solubility. The materials presented alkaline pH and released calcium ions. ZrO2 micro radiopacifier may be considered a potential substitute for Bi2O3 when associated with CSC or CSCR. The proposed materials, especially when associated with ZrO2, are potential materials for use as alternatives to MTA.

Physicochemical properties of calcium silicate cements associated with microparticulate and nanoparticulate radiopacifiers.

An experimental study was conducted to investigate the effects of using binary, ternary, and quaternary cementitious blends of portland cement (PC), fly ash (FA), ground granulated blast furnace slag (GBS), silica fume (SF), and metakaolin (MK) on initial and final setting times of self-compacting concretes (SCCs). For this purpose, a total of 65 SCC mixtures were prepared at two different water binder ratios. Furthermore, based on the experimental results, neural network (NN) model-based explicit formulations were developed to predict the initial and final setting times of SCCs in terms of the amount of concrete constituents, namely mixing water, PC, FA, GBS, SF, MK, fine (fa) and coarse (ca) aggregates, and superplasticizer (SP). The test results have revealed that the mineral admixtures were very effective on the initial and final setting times of SCCs. Besides, it was found that the model developed by using NN seemed to have a high prediction capability of initial and final setting times of SCCs.

C H Larsinos

Papers

Influence of mixing water on the setting time of concrete