High-strength Portland cement concrete has a high risk of spalling in fire. Geopolymer, an environmentally friendly alternative to Portland cement, is purported to possess superior fire-resistant properties. However, the spalling behaviour of geopolymer concrete in fire is unreported. In this paper, geopolymer and Portland cement concretes of strengths from 40 to 100 MPa were exposed to rapid temperature rises, simulating fire exposures. Two simulated fire tests, namely rapid surface temperature rise exposure test and standard curve fire test, were conducted. In both types of test, no spalling was found in geopolymer concretes, whereas the companion Portland cement concrete exhibited spalling. This can be attributed to different pore structures of the two concretes. The sorptivity test found that geopolymer concrete had a significantly higher sorption, therefore more connected pores, than Portland cement concrete when compared at the same strength level. Hence, it is suggested that the water vapour can escape from the geopolymer matrix quicker than in Portland cement concrete, resulting in lower internal pore pressure. The paper concludes that, when compared at the same strength level, the geopolymer concrete possesses higher spalling resistance in a fire than Portland cement concrete due to its increased porosity.

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SUMMARYConcrete spalling can cause severe damage to concrete structure when exposed to fire. The spalling mechanisms are not very well understood. For the testing of spalling, full-scale structural members should be used, as spalling tests are sensitive to size effects. Full-scale testing in large furnace is costly and is not suitable for testing large number of concrete mixture trials. The standard and hydrocarbon fire time-temperature curves have rapid temperature rise during the initial phase. This temperature rise requires a gas furnace with high heating capacity and cannot be generated by electric muffle furnace commonly available in many laboratories.This paper presents a method to carry out spalling test in small-scale specimens with exposure to rapid temperature rise using a commonly available electric furnace in the laboratories. The tests are based on 150 mm diameter cylinders that are laterally confined to simulate full-scale structural members. The cylinder surface is exposed to rapid temperature rise by exposing through vertical and/or horizontal holes in pre-heated small electric furnace. Some unconfined 100 mm diameter cylinders were also exposed horizontally to test the performance of confinement. The paper shows that the hydrocarbon fire and standard fire exposure can be simulated by manipulating the exposure location of the surface of the concrete cylinder. Ordinary Portland cement concrete cylinders with different strengths were tested and different spalling patterns were observed. The spalling patterns matched the test results from a gas furnace fire test simulating the fire curves. The tests demonstrated that the method is an effective and convenient technique to predict the spalling risk of a concrete.

In order to solve the problem of low accuracy caused by instability and springback during the single point incremental forming (SPIF) process, static pressure support (SPS) and ultrasonic vibration (UV) are introduced into the technology for auxiliary forming. In order to qualitatively and quantitatively study the mechanism of static pressure support–ultrasonic vibration-single point incremental forming (SPS-UV-SPIF) force, a typical truncated cone is used as the research object. The working principle and motion rules of the technology are analyzed. The sheet micro-element of the sidewall area is taken as an analysis object. The spatial stress balance equation of the sheet is constructed. The various stresses are integrated and calculated. The forces in each area of the sheet are analyzed and modeled. Finally, an analytical model for SPS-UV-SPIF force is established. The influence law of the static pressure parameter and the vibration parameter on the forming force is obtained. The corresponding SPS system and UV system are designed. The Kistler forming force test system is built. The experimental results are consistent with the theoretical analysis results, which verifies the correctness of the analytical model.

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