1、 3535 单词 ,18300 英文字符， 4760 汉字 出处： Fall M, Samb S S. Effect of high temperature on strength and microstructural properties of cemented paste backfillJ. Fire Safety Journal, 2009, 44(4): 642-651. Effect of high temperature on strength and microstructural properties of cemented paste backfill Fall M, S
2、amb S S Abstract The main purpose of this research is to investigate the inuence of high temperatures on the strength and microstructure (e.g. pore structure, porosity) of cemented paste backfill (CPB) through a series of experimental tests. A laboratory experimental setup allowing the simulation of
3、 various high-temperature conditions is developed. Different types of CPB specimens are exposed to different high temperatures (100, 200, 400 and 600 ). The strength, porosity, pore size distribution and water absorption of these CPB specimens are then evaluated by laboratory tests. Thermogravimetri
4、c and differential thermal analyses are also performed to study the thermal behaviour of the CPBs exposed to high temperatures. The results show that high temperatures have a significant effect on the properties of CPBs. Generally, increasing temperatures up to 200 leads to higher strength in most t
5、ypes of CPB studied. The porosity and pore size distribution of the CPBs change only slightly. Above 200 , the temperature reduces the strength of the CPBs. The most notable strength decrease takes place at exposure temperatures exceeding 400 . The significant decrease of the strength of the CPB is
6、accompanied by a significant change in the microstructure (porosity, pore size distribution, mineral phases). Moreover, the effect of high temperatures on the strength and microstructure of CPBs depends on the water/cement ratio (w/c ratio) and the tailings type。 Keywords:Cemented paste backll；Fire；
7、Temperature；Strength； Microstructure；Tailings 1 Introduction During the last decade, cemented paste backfills (CPBs) have become increasingly popular in underground mining operations around the world 1-5. CPB technology is considered superior to traditional hydraulic backfill methods in terms of bot
8、h economic and environmental benefits 1-7. Its application is very useful in ground support and maximizing the safe and economic recovery of ore. Indeed, in mining operations, when ore bodies are extracted, large voids are created and massive pillars are left in place for stability. Ore pillars that
9、 are left in mines represent a loss of resources, but open stopes often cause severe surface subsidence 8. The backfilling of the underground voids improves the stability, enabling safer and more efficient mining of the surrounding areas. A well-designed CPB will minimize losses imposed by leaving n
10、umerous pillars, and also improve support of the overlaying surface 8. Additionally, CPB technology is an effective means of disposal and management of tailings (finely ground rock waste product that remains after the minerals have been extracted from ore), since underground storage of CPBs can redu
11、ce the volume of tailings stored at the surface by up to 60% 5. It also minimizes the need for constructing large tailings dams at the surface 9 and thus,reduces significantly, the costs associated with surface tailings management. CPBs typically consist of a mixture of dewatered tailings (generally
12、 composed of fine silt-size particles) from the milling or processing perations of the mine, water and hydraulic binders. The binder content is usually 3-7% by weight. The proportion of the solid (tailings+binder) is between 70% and 85% by weight. These components are combined and mixed on the surfa
13、ce and transported (by gravity and/or pumping) to the underground mine workings, where the CPB can be used for the roles previously mentioned. An important parameter in judging the quality of the hardened paste backfill is its uniaxial compressive strength (UCS). Indeed, the UCS of the hardened back
14、fill is often used in the practice to evaluate its stability or structural integrity 10 since the test is relatively inexpensive and can be incorporated into routine quality control programs at the mine 11. The function of the CPB has a considerable effect on the required mechanical (strength) respo
15、nse. For example, when the CPB is used simply to fill voids or for underground disposal, in order to eliminate the risk of liquefaction at an early age, strength values between 150 and 300 kPa of the backfill are used as target values at several mines sites 12. However, in cut and fill mining, the 2
16、8-day compressive strength that is required to maintain backfill stability is generally lower than 1 MPa 3. When the paste backfill is used for roof support, strength values higher than 4 MPa are generally required. However, compressive strength is not the only signifi- cant parameter showing the st
17、ructural integrity of CPB； the microstructure of CPB strongly inuences its strength and uid transport ability (i.e. durability). Indeed, it is widely accepted that the service life and integrity of cemented materials or structures are strongly inuenced by its uid transport properties (permeability,
18、sorptivity, diffusivity) 13-15. For example, the ingress of potentially deleterious (harmful) materials, such as sulphate and oxygen by diffusion and/or capillary transport, can lead to the degradation of the cemented matrix of CPBs or a reduction of strength by sulphate attack 16-18. As a result of
19、 the increased and intensive use of CPBs in underground mining operations, several studies 1-12,15-23 have been conducted to better understand the properties (e.g. strength, microstructure) and determine different factors that can affect the properties. These studies reveal that different factors ca
20、n affect the properties (strength, microstructure) of a given CPB 8,10,11,15, such as the characteristics of different CPB compo- nents (tailings, cement, water), geomechanical conditions in the mine 3,4,6,10,11 and curing conditions 23. However, all of these studies performed on the performance pro
21、perties of CPBs have ignored the effect of fire or high temperatures on CPB properties. Additionally, most of the available results resulting from studies on the effect of high temperatures on the properties of cemented material were implemented for normal concrete 24-28. Thus, since CPB is differen
22、t from normal concrete 11,22, these results may not be suitable. This means that there is a lack of knowledge on the fire or high-temperature resistance of CPBs. Considering the fact that CPBs are sometimes exposed to high temperatures, this lack of knowledge needs to be resolved.The main sources of
23、 high temperatures in underground mine operations are mine fires and self-heating of the sulphidic rock masses adjacent to or surrounding the CPB structures, due to the oxidation of the sulphide minerals 29. Additionally, intensive cracking or the collapse of CPB structures, permitting large amounts
24、 of air to access reactive moist paste, can lead to the self-heating of the CPB as observed in various Canadian underground mines 29. Hence, considering the facts mentioned above, the main objectives of this research are to experimentally study: the effect of high temperatures on the strength of CPB
25、s, the effect of high temperatures on the microstructure of CPBs and the development of the performance of CPBs when exposed to high temperatures. Following this introduction, the materials used, a description of the developed experimental setup and the experimental tests performed are presented. Then the results are presented and discussed. Finally, the main conclusions are provided.
