Filtern
Dokumenttyp
Sprache
- Englisch (4)
Schlagworte
- Acoustic emission (4) (entfernen)
Organisationseinheit der BAM
Two fly ash-based geopolymer concretes with quartz aggregates or with expanded clay (lightweight) aggregates were exposed to the ISO 834-1 standard fire curve in a small-scale fire test set-up. Acoustic emission measurements during fire exposure and subsequent cooling were employed to study spalling events and cracking during the tests. Optical microscopy and additional acoustic measurements were conducted after the testing to better understand the crack propagation in the samples. The testing revealed that neither of the concretes were susceptible to spalling, which is particularly notable for the concrete with quartz aggregates, as it is a high-strength concrete. This behavior is attributed to the relatively high permeability of the concretes and their low amount of chemically bound water. Significant crack formation was detected only around the temperature of the alpha–beta quartz transition (573 °C) and on cooling. Because of aggregate deformations at the quartz transition temperature, deterioration after heating was more significant in the geopolymer concrete with quartz aggregates. Crack formation also occurred in the concrete with expanded clay aggregates, caused by shrinkage of the geopolymer paste on cooling. Acoustic emission measurements proved to be a valuable tool to investigate processes during high temperature exposure.
The present study aims to investigate the use of geopolymer mortars as passive fire protection system for steel structures. Coal fly ashes were used as aluminosilicate source and perlite was employed as aggregate to obtain a lightweight system. In addition, a geopolymer mortar containing quartz aggregate was produced for comparison. The geopolymer mortars were applied on stainless steel plates and exposed to both, cellulosic and hydrocarbon standard fire curves, according to ISO 834-1 and EN 1363-2, respectively. Acoustic emission measurements were conducted to analyze cracking phenomena during the high temperature exposure. The resulting temperature-time curves showed that the investigated system is effective in retarding the temperature rise of the steel plates. When the cellulosic fire curve was applied, a 20 mm [0.79 in.] thick layer of lightweight geopolymer mortar protected the steel substrate from reaching the critical temperature of 500 °C [932 °F] for at least 30 minutes, avoiding the rapid decrease of its mechanical properties and thus representing an important safety measure against accidental fires. No spalling phenomena on heating were detected; however, significant cracking was observed on cooling.
This study aims at investigating the use of coal fly ash-based alkali activated mortars as passive fire protection system for steel structures. These systems are used to slow down the temperature rise of the steel substrate in case of fire. In addition, the protective system should guarantee the ability to prevent and/or mitigate steel corrosion phenomena. The behavior of a light-weight mortar was compared to that of a normal-weight mortar. Density and porosity were measured to better characterize the physical properties of the mortars. The degree of protection in case of fire was assessed by performing medium-scale fire tests. Acoustic emission measurements were conducted to analyze cracking phenomena during the high temperature exposure. The corrosion process was evaluated using an electrochemical approach in order to monitor the durability of the developed material. Preliminary results show that a 20 mm-thick layer of light-weight mortar is able to protect the steel substrate from reaching the critical temperature of 500 °C for 38 minutes in case of cellulosic fire. In addition, alkali activated mortars provide protection for carbon steel in presence of aggressive environment (i.e. presence of chlorides). The corrosion resistance is strictly related to the physical properties of the developed mortars.
Alkali-activated fly ashes have been proposed for various applications where resistance against high temperatures is required, yet several details regarding the response of these materials to heat-exposure need to be clarified. In the present study, heat-induced cracking in fly ash-based alkali-activated pastes and lightweight mortars was analyzed by in-situ acoustic emission (AE) detection during complete heating-cooling cycles (up to ∼1100 °C), augmented by thermogravimetry and ex-situ SEM and XRD analyses. The applicability of the lightweight mortars as passive fire protection coatings was assessed by recording temperature-time curves of mortar-coated steel plates. Cracking during heating was limited and associated exclusively with the dehydration of the materials in the temperature range ∼90–360 °C. However, samples heated to temperatures above ∼600 °C exhibited intense cracking on cooling. This was attributed to differential deformations caused by local sintering and partial melting at the glass transition temperature, and subsequent quenching on cooling.