Papers by Keyword: Explosive Spalling

Abstract: This article is focused on issues of concrete behavior under high temperatures. The aim of this work is to verify the influence of the addition of organic fibres on the fire resistance of concrete. Emphasis is placed on describing the possibility of using recycled fibres from PET or cellulose due to the positive ecological impact. Based on the obtained results, it is clear that it is possible to use fibres to increase fire resistance even from sources that do not come from primary production.

Abstract: Concrete is considered as a non-combustible building material. However, at High-Performance Concrete (HPC) is due to its dense structure more likely to occur in explosive spalling. This results in lost of load bearing capacity function of concrete. This paper deals with design, production and testing of the cement-based concrete with the use of different fibers (polypropylene fibers and cellulose fibers). It also assesses the influence of high temperature on strength, visual changes of specimens, changes of surface and degradation of testing specimens due to heat loads according to normative heat curve and also according to hydrocarbon curve.

Abstract: Permeability of concrete is a good indicator of the risk of explosive spalling, concrete with low permeability is more prone to explosive spalling. To study explosive spalling of concrete, experimental tests on the concrete permeability have been carried out at ETH. The influences from temperature and moisture content have been investigated. The permeability of concrete is found to increase with the temperature and to decrease with moisture content. Based on the test results, a permeability model has been proposed. The explosive spalling has been predicted and an engineering boundary permeability for the liability to spalling is recommended to be 2 × 10^-17 m² for a concrete slab heated according to ISO fire curve. The boundary permeability is influenced by moisture content, tensile strength and heating rate.

Abstract: This paper is focused on clarifying behaviour of concrete at elevated temperature with employing new test set-up constructed at Institute of Building Construction and Technology, Vienna University of Technology. This unique test set-up allows measuring gas permeability of different building materials such as concrete or ceramic at both high temperature (up to 400°C) and pressure (up to 6 bars). Present paper illustrates a new set up for permeability measurement during the heating and cooling and different testing procedures and evaluation of their influence on results.

Abstract: The paper presents the application of ultrasound measurements for the determination of structural alterations of concrete exposed to fire. Concrete is evaluated as an incombustible material, class A1, but the high exposure temperature, like in fire, may cause cracks and changes of internal structure. The ultrasound measurement is a nondestructive method. It is possible to measure ultrasound velocity before and after thermal loading. The ultrasound measurement could be used also at building side as to detect structural alterations after a fire or imperfection in concrete elements. Three different concrete mixtures were prepared and tested in this study. The basalt aggregate were used in the reference mixture and in a mixture with addition of polypropylene fibers (PP-fibers). The third concrete was made with light weight aggregates (LWA). The test slabs (dimension 10 × 30 × 1150 mm) were poured and cured in laboratory ambient (22°C and 40% RH) for 3 months. Then the slabs were exposed to fire, according to standard temperature-time curve ISO 834. The ultrasound velocity was determined on crossline screen of 10 points before and after heating of the concrete slabs. The results of ultrasound measurements indicate the changes of internal concrete structure. The cracks are formed by pressure of evaporating unbounded water and thermal extensibility of single components.

Abstract: Fire resistance of concrete structures could be improved by add of polypropylene fibres in to the concrete mixture in butch from 1 to 2 kg per 1 m³ of fresh concrete. This method is effective, but it is not possible to use it for existing concrete and existing reinforced concrete structures. The new method which has good potential for fire protection of existing structures is based on creation of capillary pore and micro cracks system, which allowed water vapour evaporate from concrete. This study deals with determination of appropriate temperature in which is created adequate network of capillary pores and micro cracks which has no influence on strength and durability of the concrete. The formation of macro cracks and bigger pores could cause rapid reduction of compressive and tensile strength, decrease of resistance to aggressive substances and decrease of the frost resistance. The high performance concrete (HPC) has very low porosity, which can cause explosive spalling while the water vapour tries to evaporate from concrete structure during the fire. The HPC concrete has high compressive strength and high density. The HPC samples were exposed to temperatures 150, 250, 350 a 450°C, and after cooling down to normal ambient were carried out tests to define changes in porosity by mercury porosimetry, mass looses and compressive strength changes. The heated HPC concrete is regaining humidity into its structure from surrounding atmosphere, which can cause rehydratation of some chemical compounds. [1] For verification of these hypotheses the HPC samples were kept in water storage for 4 weeks and then tested.

Abstract: An experimental investigation was conducted on behavior of high performance steel-fiber concrete subjected to high temperature, in terms of explosive spalling and permeability. A series of concretes incorporated steel fiber at various dosages were prepared, and further processed to have a series of moisture contents. Explosive spalling tests were conducted on control plain concrete and steel fiber concrete. After explosive spalling tests, each of the specimens that didn’t encounter spalling was sawn into two pieces. Crack observations and permeability tests were conducted on the sawn surfaces. The results prove that steel fiber is efficient to avoid spalling concrete under high temperature. The permeability increases significantly after thermal exposure, while it also exhibits an ascending trend with the increase of moisture content. Therefore it is concluded that steel fiber can play a positive effect on explosive spalling of high performance concrete under high temperature, as well as on permeability after thermal exposure.

Abstract: A reliability analysis was conducted on high-strength concrete (HSC) columns during a fire. The influences of fire’s randomness and explosive spalling of concrete were investigated. The fire resistance for axial loading capacity of HSC columns was in terms of steel yield strength and concrete compressive strength with considering the effect of elevated temperatures. The load random variables included dead load and sustained live load. The JC method was applied to calculate the reliability index of the fire resistance of axially loaded HSC columns. It was found that the randomness of fire and explosive spalling of concrete had a significant influence on reliability of HSC columns.

Abstract: High performance concrete (hereafter, HPC) is well known by its high compressive strength, strong resistance to deformation and excellent durability. Whereas, HPC is prone to spall when exposed to high temperatures and it probably results in sharp reduction of the fire resistance and loading capacity of HPC elements and structures. This paper presents a summary of research achievements on fire-resistance behavior of HPC in the past 10 years including the mechanical behavior degradation, analysis of spalling mechanism, effect of various types of fiber and other factors influencing the post-fire properties of HPC material as well as structural behavior of HPC elements. Studies on micro-structure of HPC have been carried out, which will help build a more sophisticated recognition of its performance under high temperatures. In spite of the large number of research results, more improvement on HPC material and HPC structures are still needed because of the devastating consequences caused by strength degradation or spalling-to-collapse. Thus in this paper a new idea of HPC-composite structures is proposed, expected to decrease the probability of spalling.

Abstract: The paper presents results of experimental and numerical analyses on the fire behavior of concrete elements protected by sprayed protective linings. Particular attention is given to high- (HPC) and ultrahigh performance concrete (UHPC), as HPC and UHPC tend to exhibit explosive spalling in fire due to low porosity. The results provide basic input data for the development of simplified rules for the fire design of concrete structures protected by sprayed protective linings.