SUMMARYThe high temperature performance up to 800 • C of combined fly ash (FA) and slag geopolymers at the ratio of 100, 65/35, 50/50, 35/65 and 100% (wt-%) is presented in this paper. Geopolymers are alternative novel binders to conventional Portland cement and are generally believed to provide superior fire resistant properties due to their ceramic-like characteristics. This paper presents new data on the behavior of geopolymers made with combined FA/slag mentioned previously, which were mixed with alkaline materials with molecular silicate modulus (Ms = SiO 2 /Na 2 O) of 0, 0.5, 1.0, 1.5 and 2.0 with sodium (Na) dosages of 4 and 8 (wt-%). Altogether 60 mixes were made yielding compressive strengths between 3 and 83 MPa. Behavior of the material to high temperatures was investigated by exposing the specimens to 800 • C and testing for compressive strengths. It was found that as the initial strength increases, the residual strength exponentially decreased. The compressive stress versus strain relationships showed that the ductility of the specimens decreased as the initial strength increased. The ability of the materials with high ductility (i.e. less brittleness) to accommodate thermal incompatibilities arising from uneven temperatures arising during heating is concluded to be the major factor contributing to the reduced strength losses. Geopolymer has recently emerged as a novel engineering binder material with the potential to form an element of an environmentally sustainable construction product [1,2]. Geopolymers are often compared with the conventional Portland cement since the applications of geopolymers are targeted to replace the conventional Portland cement. Geopolymer is a term used to describe inorganic polymers based on alumino-silicates [3] and can be produced by synthesizing pozzolanic * Correspondence to: Maurice Guerrieri, Department of Civil Engineering, Monash University, Clayton 3800, Australia. 164M. GUERRIERI AND J. G. SANJAYAN compounds or alumino-silicate source materials with highly alkaline solutions [4]. Owing to their ceramic-like properties, geopolymers are believed to possess good fire resistance [5,6]. Geopolymers are also referred in the literature as alkali-activated fly ash (FA) or inorganic polymers [7]. The production of geopolymers has been shown to release 80 to 90% less green house gas emissions than the conventional Portland cement [2]. Each ton of conventional Portland cement production is responsible for the release of 0.7 to 1.0 tons of CO 2 into the atmosphere [8].Ground-granulated blast furnace slag (Slag) and FA, byproducts of iron manufacturing and coal burning electrical power plant industries, respectively, have been used widely either integrated or pre-blended with ordinary Portland cement (OPC) to produce blended cement binders. Slag and FA-blended cements are characterized by their low heat of hydration and high chemical durability and can enhance the physical and mechanical properties of concretes and even provide higher early strength than OPC concretes [9,1...
With a growing pipeline of major transport infrastructure projects transforming Victoria's road and rail networks, there is an increase in demand for the construction of underground tunnels using the shield tunneling method. Such tunnels need to be designed for fire resistance in order to preserve both structural integrity and serviceability in the event of a fire event. This paper describes the approach taken to design the concrete tunnel lining segments for Melbourne's Metro Tunnel Project for structural stability during a severe fire incident. Two types of fire testing programs were implemented, both of which used the RABT ZTV (rail) fire curve. The first involved the fire testing of 12 unloaded flat panels in order to determine whether a particular concrete mix design would be susceptible to spalling. Second, six prototype full scale tunnel lining segments were subjected to full scale structural fire testing, for the first time in Australia. The results indicated that full scale structurally loaded fire tests are essential as unloaded flat panels underestimate the degree of spalling. Addition of PP fibers are successful in mitigating spalling in addition to using pozzolans cements such as flyash and slag.
SUMMARYThis paper reports the effect of elevated temperature exposures, up to 1200 • C, on the residual compressive strengths of alkali-activated slag concrete (AASC) activated by sodium silicate and hydrated lime; such temperatures can occur in a fire. The strength performance of AASC in the temperature range of 400-800 • C was similar to ordinary Portland cement concrete and blended slag cement concrete, despite the finding that the AASC did not contain Ca(OH) 2 , which contributes to the strength deterioration at elevated temperatures for Ordinary Portland Cement and blended slag cement concretes. Dilatometry studies showed that the alkali-activated slag (AAS) paste had significantly higher thermal shrinkage than the other pastes while the basalt aggregate gradually expanded. This led to a higher thermal incompatibility between the AAS paste and aggregate compared with the other concretes. This is likely to be the governing factor behind the strength loss of AASC at elevated temperatures.
SummaryThis paper attempted to isolate variables that govern concrete spalling when exposed to a hydrocarbon fire. The influence of specimen size was investigated by studying 4 specimen sizes consisting of cylinders, columns, and panels. Three aggregate sizes, 7 mm, 14 mm, and 20 mm were used in the concrete mixes to determine their effect on concrete spalling. Influence of aggregate type on concrete spalling was also investigated. Forty-two different specimens were considered in this investigation. Concrete spalling was quantified as nominal spalling depth, which has been presented as a new way of quantifying the degree of concrete spalling. The results indicated that specimen size did have an effect on the spalling of concrete under hydrocarbon fire exposure and that nominal spalling depth of concrete increases as the specimen size increases.Aggregate size effect was evident when the maximum aggregate size increased from 7 mm to 20 mm, and explosive spalling was more severe for specimens with small size aggregates. Specimens with 14-mm aggregate size showed inconsistent results and the spalling behavior witnessed was more random and sporadic. The type of aggregate used has no clear bearing on concrete spalling given both aggregates had similar linear expansion profiles. However, concrete is susceptible to a less known phenomenon termed spalling in fire. Spalling of concrete in fire is the dislodgement of small pieces of concrete up to 50 mm (popping out) from the surface of the concrete, often explosive in nature. If the degree of spalling is significant, the load bearing capacity of the concrete member can be reduced due to (1) reduction in its cross-sectional size, and (2) rapid increase in temperatures of the reinforcement. more predominate when concrete is subjected to hydrocarbon fire due to the rapid heating rise. 5 The moisture content of the specimen has been reported to be a significant factor which governs spalling. 6High levels of moisture content generate the buildup of pore water pressures.A number of key researchers have studied the factors which govern spalling including thermal stresses, pore pressures, thermal dilation, and incompatibility between cement paste and aggregate. 7-10 The "moisture-clog mechanism" due to the buildup of pore water pressures has been widely accepted as the main mechanism causing concrete spalling. 9,[11][12][13][14][15][16][17] Contrary to this, spalling caused by differential thermal gradients within the concrete element has also been widely accepted to explain the spalling phenomenon. crack of critical size and orientation increases with the volume of the specimen. [22][23][24] This is in agreement with Bazant's size effect law (SEL) theory, which states that as the specimen size increases, the compressive strength decreases. 23,25,26 In relation to spalling, the "size effect" phenomenon has a direct effect on the moisture content of the concrete specimen, the rate of in situ heating, and water mass loss. | EXPERIMENTAL PROGRAMMEThe materials used in this investig...
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