Effect of high temperature and cooling regimes on the compressive strength and pore properties of high performance concrete

doi:10.1016/S0950-0618(00)00031-3

Construction and Building Materials

Volume 14, Issue 5, July 2000, Pages 261-266

https://doi.org/10.1016/S0950-0618(00)00031-3 Get rights and content

Abstract

This paper describes the behavior of high performance concrete (HPC), compared with normal strength concrete (NSC), after subject to different high temperatures (800 and 1100°C) and cooling regimes (gradual and rapid cooling). Deterioration of compressive strength of the concrete was measured. The results obtained showed that the strength of both the HPC and NSC reduced sharply after their exposure to high temperatures. Thermal shock due to rapid cooling caused a bit more deterioration in strength than in the case of gradual cooling without thermal shock. However, thermal shock did not significantly increase the spalling of HPC. Mercury intrusion porosimetry (MIP) tests were carried out to measure changes in the pore size distribution in the concrete. Test results showed that the pore volume in the HPC increased much more than that in the NSC. A significant change in the cumulative pore volume was observed and the difference in cumulative pore volume between the two cooling regimes was less after subject to the peak temperature of 1100°C when compared with that of 800°C peak temperature.

Introduction

Concrete has been the leading construction material for nearly a century. High performance concrete (HPC) with high strength or high durability is gradually replacing the normal strength concrete, especially in structures exposed to severe environment. The advantages of HPC result from the improvement of internal structure of the material as compared with that of the normal concrete [1]. The dense microstructure of HPC ensures a high strength and a very low permeability. The low permeability is probably essential to obtain good durability in severe exposure conditions where there are aggressive agents such as chloride, sulfate, etc. However, the dense microstructure of HPC seems to be a disadvantage in the situation where the HPC is exposed to fire. Recent fire test results show that there is a great difference between the properties of HPC and normal concrete after being subjected to high temperature [2], [3], [4]. It was observed that HPC, especially high strength concrete (HSC) is susceptible to spalling, or even explosive spalling when subject to rapid temperature rise such as in the case of a fire [5], [6]. Experimental studies have also shown that spalling of HPC is influenced by many complicated factors, such as rate of temperature elevation, mineral constituents of aggregates, thermally induced mechanical stress, density of concrete, moisture content, etc. Although the failure mechanisms of HPC spalling have not been sufficiently understood, there are two mechanisms which are considered as the direct causes of spalling of HPC. One is the thermal stress induced by the rapid temperature rise or thermal shock [7]; the other is the water vapor, which may cause high pore vapor pressure [8]. The properties of this binder are, therefore, critical to the HPC. In this study, three grades of HPC and one NSC were tested for their compressive strength after exposure to different high temperatures and cooling regimes. The variation in the microstructures of both the HPC and NSC were tested by means of mercury intrusion porosimetry (MIP).

Section snippets

Materials and test methods

Ordinary Portland cement conforming to BS12:1991, crushed granite with a maximum size of 20 and 10 mm, superplasticizer based on naphthalene sulfonates complying with BS5075 part3:1985, silica fume, pulverized fly ash (PFA) meeting the requirements of BS3892 part1:1982, as well as steel and polypropylene fibers were adopted in this study. The chemical compositions and physical properties of cement, silica fume and fly ash are given in Table 1.

The length and aspect ratio are 25 mm and 60,

Test results and discussion

As shown in Fig. 1, compressive strength of the HPC decreased more sharply than that of the NSC. Control sample referred to the standard cured specimen that was tested at 90 days and not subjected to high temperatures. When temperature was elevated to 800°C, the residual strength percentage of the HPC was 26–34% for the gradual cooling and 22–28% for the rapid cooling. When the peak temperature was 1100°C (Fig. 2), the residual strength percentage of HPC was 8–12% for gradual cooling and 8–10%

Conclusions

1.
When subjected to the peak temperature of 800°C, the residual compressive strength of HPC dropped to approximately 26–34% of the original after the gradual cooling process and 22–28% after the rapid cooling; when subjected to 1100°C, the residual strength of HPC reduced to approximately 8–12% for gradual cooling and 8–10% for rapid cooling.
2.
Steel fiber could reduce the deterioration of concrete to an extent. Polypropylene fiber used to prevent spalling of HPC did not lead to a marked degradation

Acknowledgements

The authors would like to thank the Hong Kong Polytechnic University for supporting the research work. This research was also part of a project financed by the Chinese National Nature Science Foundation. The support from the State Key Laboratory of Mineral Deposit Research, Nanjing University is also acknowledged.

References (16)

R. Breitenbücher
Developments and applications of high-performance concrete
Mater Struct
(1998)
Diederichs U, Jumppanen UM, Penttala V. Material properties of high strength concrete at elevated temperatures, IABSE...
Morita T, Saito H, Kumagai H. Residual mechanical properties of high strength concrete members exposed to high...
Furumura F, Abe T, Shinohara Y. Mechanical properties of high strength concrete at high temperatures. Proceedings of...
C. Castillo et al.
Effect of transient high temperature on high-strength concrete
ACI Mater J
(1990)
G. Sanjayan et al.
Spalling of high-strength silica fume concrete in fire
ACI Mater J
(1993)
Ahmed GN, Hurst JP. An analytical approach for investigating the causes of spalling of high-strength concrete at...
Khoylou N, England G. The effect of elevated temperatures on the moisture migration and spalling behavior of...

There are more references available in the full text version of this article.

Cited by (123)

Research on uniaxial mechanical performance of high-performance concrete after high temperature rapid cooling and damage mechanism analysis
2024, Journal of Building Engineering
High-performance concrete (HPC) is widely used in civil and hydraulic engineering, with durability as its main indicator. During the service life of high-performance concrete structures, there is a risk of extreme fire incidents. The fire department generally adopt water cooling to quickly control the fire after a fire occurred. Studying the mechanical property of high-performance concrete after high temperature and rapid cooling is of great significance for evaluating the safety performance of high-performance concrete structures after a fire. Therefore, three types of uniaxial loading modes (uniaxial compression, pure shear, uniaxial tension) and five temperatures (20^OC, 200^OC, 400^OC, 600^OC, 800^OC) were considered in this study. Hydraulic servo machine was used to conduct experimental research on the uniaxial mechanical properties of high-performance concrete after high temperature and rapid cooling. In addition, digital image correlation (DIC) and acoustic emission technology (AE) were combined to analyze the external and internal damage evolution processes of concrete during loading process. The experimental results are as follows: as the temperature increases, the compression strength of high-performance concrete under uniaxial compression is initially increased and then decreased, with a maximum reduction of 62.02%; however, the strength of high-performance concrete under pure shear and uniaxial tension conditions are gradually decreased, with maximum reduction of 76.12% and 81.26% respectively; compared to room temperature cooling conditions, the strength of high-performance concrete under water cooling condition is decreased more greatly, but this difference gradually decreases with the increase of temperature; combined with the analysis of DIC and AE, under different stress states, the surface main cracks of HPC become more tortuous and accompanied by more micro-cracks under the influence of high temperature, and the evolution process of cracks inside HPC also changes significantly with the temperature. At the same time, the surface damage process of HPC under the influence of load has obvious lag compared with the internal damage process. Finally, based on the cumulative ringing count obtained by AE, the damage process of high-performance concrete under different loads is characterized, and the constitutive model of high-performance concrete after high temperature and rapid cooling under different loading modes is established. The research results provide a theoretical basis for the safety evaluation and calculation of high-performance concrete structures after fire.
General and optimal 2D convolutional neural networks to predict the residual compressive strength of concretes exposed to high temperatures
2024, Engineering Applications of Artificial Intelligence
High temperature severely deteriorates the durability and mechanical properties of concrete. Experimental tests to obtain the compressive strength of fire-damaged concretes are costly and time-consuming. Soft computing techniques can be used to estimate the residual compressive strength of concretes rapidly and accurately. This study developed three general, optimal and accurate 2D convolutional neural network (CNN) models to predict the compressive strength of fire-damaged concretes. The data set contained 1062 samples, split randomly into the training (60%), validation (20%) and verification (20%) sets. The inputs included mixture proportion, chemical compositions of cementitious materials, specimen shape and size, heating regime (peak temperature, heating rate and exposure time) and age. The residual compressive strength was the output. The 28-day and unheated compressive strengths were the supplementary inputs in two of the models. The genetic algorithm optimized the models' architecture, including the layers’ number and their hyperparameters. All three models showed acceptable accuracy; however, considering the supplementary inputs enhanced the accuracy slightly. The R², RMSE, MAE, MAPE and VAF values of the verification set in the model considered the 28-day compressive strength as the supplementary input feature were 0.965, 4.80 MPa, 3.48 MPa, 12.83%, and 96.35%, respectively. The sensitivity analysis revealed that the heating regime, especially peak temperature, is the most fundamental input feature. Finally, the superiority of the proposed models over the previous studies was shown based on data set size and statistical metrics.
Investigation of the effect of different curing conditions on the mechanical performance of calcium aluminate cement concrete at elevated temperatures
2023, Construction and Building Materials
Research on improving the performance of concrete at elevated temperatures has been increasing in recent years. In this context, Calcium Aluminate Cement (CAC) can be used in concrete mixes to increase the performance of concrete at elevated temperatures. However, the use of CAC has not yet become widespread in structural applications due to the unstable nature of CAC, which is highly affected by curing temperature and humidity. Therefore, it is of great importance to investigate the curing conditions that directly affect the unstable nature of CAC. In the present study, different curing methods were applied to calcium aluminate cement concretes (CACC) and their performance at elevated temperatures (300 °C, 600 °C, 900 °C) was investigated. In this framework, compressive strength, modulus of elasticity and flexural strength of the samples were determined, load–displacement relations and microstructural changes were evaluated. As a result of the study, it has been determined that CACC samples have better mechanical performance than normal concrete at elevated temperatures and especially the mechanical performance of CACC samples cured at high temperature (CACCH) is better than CACC samples cured under normal conditions (CACCN).
Comparative study of genetic programming-based algorithms for predicting the compressive strength of concrete at elevated temperature
2023, Case Studies in Construction Materials
The elevated temperature severely influences the mixed properties of concrete, causing a decrease in its strength properties. Accurate proportioning of concrete components for obtaining the required compressive strength (C-S) at elevated temperatures is a complicated and time-taking process. However, using evolutionary programming techniques such as gene expression programming (GEP) and multi-expression programming (MEP) provides the accurate prediction of concrete C-S. This article presents the genetic programming-based models (such as gene expression programming (GEP) and multi-expression programming (MEP)) for forecasting the concrete compressive strength (C-S) at elevated temperatures. In this regard, 207 C-S values at elevated temperatures were obtained from previous studies. In the model’s development, C-S was considered as the output parameter with the nine most influential input parameters, including; Nano silica, cement, fly ash, water, temperature, silica fume, superplasticizer, sand, and gravels. The efficacy and accuracy of the GEP and MEP-based models were assessed by using statistical measures such as mean absolute error (MAE), correlation coefficient (R²), and root mean square error (RMSE). Moreover, models were also evaluated for external validation using different validation criteria recommended by previous studies. In comparing GEP and MEP models, GEP gave higher R² and lower RMSE and MAE values of 0.854, 5.331 MPa, and 0.018 MPa respectively, indicating a strong correlation between actual and anticipated outputs. Thus, the GEP-based model was used further for sensitivity analysis, which revealed that cement is the most influencing factor. In addition, the proposed GEP model provides simple mathematical expression that can be easily implemented in practice.
Effect of cooling methods on the residual properties of concrete exposed to elevated temperature
2022, Results in Engineering
One of the most damaging effects a building may suffer is a fire. Structures may be exposed to temperatures of more than 1000 °C while the fire is burning. In the course of and after the fire, structural concrete loses its rigidity and strength. The concrete's residual strength qualities may also be significantly influenced by the cooling phase's speed and cooling medium. In an attempt to compare the impact of various cooling regimes on concrete, an investigation has been made. The effects of adding polypropylene fibres and air entrainment admixtures were examined in addition to studies on traditional concrete. The water-cement ratio, cement mass and type, and aggregate type were all the same throughout the test. After cooling down from five distinct heat stages ranging from 150 to 900 °C, samples were compared to their unheated counterparts' results. Five distinct approaches, including slow cooling, forced air cooling, cooling with water mist, quenching, and the “normal” cooling under laboratory conditions, were used to study the cooling effects. The study aimed to examine integrated temperature endurance numbers, relative residual compressive strength values, and residual compressive strength values in addition to visual observation. Regulations were matched with the outcomes. The findings demonstrated that, up to 600 °C, there were no appreciable changes in the residual properties between the various cooling methods or between the different mediums with virtually the same cooling pace. The apparent disintegration of water-cooled samples was evident after cooling from 900 °C.
Effectiveness of GFRP strengthening of normal and high strength fiber reinforced concrete after exposure to heating and cooling
2022, Engineering Science and Technology, an International Journal
Damage induced by fire is considered a serious threat to reinforced concrete structures during their useful lifetime. While concrete is a non-flammable material, its exposure to fire affects its stress-strain characteristics and durability. Given that a full replacement and/or demolition option is economically inefficient for fire-damaged structures, a better alternative for lengthening their service life involves repair or strengthening the damaged members. The current testing program primarily investigated the influence of strengthening by glass fiber reinforced polymer (GFRP) sheets on the behavior of heat-damaged plain and fiber-reinforced normal and high strength concretes. Strengthening was considered for concrete cylinders after being exposed to 400 °C and 600 °C temperature and left to cool by air cooling or water quenching. Fiber-reinforced concrete (FRC) mixes were cast with steel, polypropylene, or a hybrid of steel and polypropylene fibers. For plain and various fiber-reinforced normal strength concretes exposed to 400 °C and cooled by ambient air cooling or water quenching, the compressive strength of GFRP confined concrete increased by 39% to 48% and 42% to 56%, respectively (in comparison to the unheated specimens). However, this enhancement was observed to be higher for concretes heated at 600 °C.

View all citing articles on Scopus

View full text

Effect of high temperature and cooling regimes on the compressive strength and pore properties of high performance concrete

Abstract

Introduction

Section snippets

Materials and test methods

Test results and discussion

Conclusions

Acknowledgements

Developments and applications of high-performance concrete

Mater Struct

Effect of transient high temperature on high-strength concrete

ACI Mater J

Spalling of high-strength silica fume concrete in fire

ACI Mater J