Fire resistance of corroded high-strength structural concrete

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Khaled Sobhan ◽  
Dronnadula V. Reddy ◽  
Fernando Martinez
Keyword(s):  
Compressive Strength ◽  
Mass Loss ◽  
Structural Integrity ◽  
Residential Buildings ◽  
Concrete Structures ◽  
Pulse Velocity ◽  
Design Codes ◽  
Fire Exposure ◽  
Structural Concrete ◽  
Content Type

Purpose The exposure of reinforced concrete structures such as high-rise residential buildings, bridges and piers to saline environments, including exposure to de-icing salts, increases their susceptibility to corrosion of the reinforcing steel. The exposure to fire can further deteriorate the structural integrity of corroded concrete structures. This combined effect of corrosion damage and fire exposure is not generally addressed in the structural concrete design codes. The synergistic combination of the effects of corrosion and fire forms the basis of this paper. Design/methodology/approach Concrete beam specimens with different strengths were prepared, moist-cured and corroded with impressed current. Later, they were “crack-scored” for corrosion evaluation, after which half were exposed to fire in a gas kiln. The fire damage was evaluated by nondestructive testing using ultrasonic pulse velocity. Next, all specimens were tested for residual flexural strength. They were then autopsied, and the level of corrosion was determined based on mass loss of the reinforcement. Findings For corroded specimens, the flexural capacity loss because of fire exposure increases as the compressive strength increases. In general, the higher the crack score, the higher the corresponding mass loss, unless some partial/segmental debonding of the reinforcement occurred. The degree of corrosion increases with decreasing compressive strength. The residual moment capacity, based on analytically determined capacities of uncorroded and nonfire-exposed beams, was significantly lower than those of uncorroded beams exposed to fire. Originality/value The combined effects of corrosion and fire on the mechanical properties of structural concrete are relatively unknown, and no guidance is available in the existing design codes to address this issue. Accordingly, the findings of the paper are expected to be valuable to both researchers and design engineers and can be regarded as the initial investigation on this topic.

The ability of high performance concrete to resist high temperature

2017 ◽  
Vol 8 (4) ◽  
pp. 392-401 ◽  
Author(s):  
Hassan A.M. Mhamoud ◽  
Jia Yanmin
Keyword(s):  
Compressive Strength ◽  
Flexural Strength ◽  
Mass Loss ◽  
High Performance ◽  
Elevated Temperatures ◽  
High Performance Concrete ◽  
Sharp Decrease ◽  
Test Results ◽  
Content Type ◽  
Chinese Standard

Purpose This study aims to focus on the resistance to elevated temperatures of up to 700ºC of high-performance concrete (HPC) compared to ordinary Portland concrete (OPC) with regards to mass loss and residual compressive and flexural strength. Design/methodology/approach Two mixtures were developed to test. The first mixture, OPC, was used as the control, and the second mixture was HPC. After 28 days under water (per Chinese standard), the samples were tested for compressive strength and residual strength. Findings The test results showed that at elevated temperatures of up to 500ºC, each mixture experienced mass loss. Below this temperature, the strength and the mass loss did not differ greatly. Originality/value When adding a 10 per cent silica fume, 25 per cent fly, 25 per cent slag to HPC, the compressive strength increased by 17 per cent and enhanced the residual compressive strength. A sharp decrease was observed in the residual flexural strength of HPC when compared to OPC after exposure to temperatures of 700ºC.

Assessment of mechanical and fire resistance for hybrid nano-clay and steel fibres concrete at different curing ages

2019 ◽  
Vol 11 (2) ◽  
pp. 189-203 ◽  
Author(s):  
Ola Bakr Shalby ◽  
Hala Mohamed Elkady ◽  
Elsayed Abdel Raouf Nasr ◽  
Mohamed Kohail
Keyword(s):  
Compressive Strength ◽  
Residual Strength ◽  
Low Cost ◽  
Partial Replacement ◽  
Fire Exposure ◽  
Content Type ◽  
Steel Fibres ◽  
Concrete Properties ◽  
Nano Clay ◽  
Concrete Mix

Purpose Nano-Clay (NC) is reported as a candidate partial replacement for cement, due to its abundance and relatively low cost - beside reported promotion of different concrete properties. On the other hand, Steel Fibres (SF) has proven to have a positive effect on post fire exposure residual strength of concrete. This paper aims to present the outcomes of a comprehensive research program assessing a hybrid mix between NC and SF in concrete mixtures (NCSF-CRETE). Design/methodology/approach Physical chemical and physical characterization of NC is performed using different tools as XRF spectrometer, and TEM micrograph. Fresh concrete properties of NSCF-CRETE as slump and air content are investigated. Enhancement in permeability using NSCF is verified by comparing its resistance to the penetration of chlorides resistance with regular concrete mix. Besides, the proposed NCSF-CRETE compressive strength is evaluated compared to mixes with NC and SF each used separately at different curing ages. Besides, NSCF and compared mixes are exposed to an indirect fire testing program – two hours exposure – for: 300, 450 and 600°C. Degradation in compressive strength was investigated after exposure to different temperatures and percentage of residual strength is reported. Findings Results indicated an improved performance of NCSF -CRETE of about 40% compared to regular concrete in compressive strength at normal conditions. This improvement extended to its behavior when subjected to indirect fire exposure NSCF also maintained 40% more strength than the residual in regular concrete mix – which suffered severe damage – after 2 h exposure to 600°C. Originality/value Using NCSF-Crete allows retrofitting the structure after exposure to such drastic conditions.

Experimental determination of the residual compressive strength of concrete columns subjected to different fire durations and load ratios

2020 ◽  
Vol 11 (4) ◽  
pp. 529-543
Author(s):  
Anjaly Nair ◽  
Osama (Sam) Salem
Keyword(s):  
Experimental Study ◽  
Compressive Strength ◽  
Reinforced Concrete ◽  
Concrete Columns ◽  
Fire Exposure ◽  
Fire Performance ◽  
Content Type ◽  
Residual Compressive Strength ◽  
Standard Fire ◽  
Strength Capacity

Purpose At elevated temperatures, concrete undergoes changes in its mechanical and thermal properties, which mainly cause degradation of strength and eventually may lead to the failure of the structure. Retrofitting is a desirable option to rehabilitate fire damaged concrete structures. However, to ensure safe reuse of fire-exposed buildings and to adopt proper retrofitting methods, it is essential to evaluate the residual load-bearing capacity of such fire-damaged reinforced concrete structures. The focus of the experimental study presented in this paper aims to investigate the fire performance of concrete columns exposed to a standard fire, and then evaluate its residual compressive strengths after fire exposure of different durations. Design/methodology/approach To effectively study the fire performance of such columns, eight identical 200 × 200 × 1,500-mm high reinforced concrete columns test specimens were subjected to two different fire exposure (1- and 2-h) while being loaded with two different load ratios (20% and 40% of the column ultimate design axial compressive load). In a subsequent stage and after complete cooling down, residual compressive strength capacity tests were performed on each fire exposed column. Findings Experimental results revealed that the columns never regain its original capacity after being subjected to a standard fire and that the residual compressive strength capacity dropped to almost 50% and 30% of its ambient temperature capacity for the columns exposed to 1- and 2-h fire durations, respectively. It was also noticed that, for the tested columns, the applied load ratio has much less effect on the column’s residual compressive strength compared to that of the fire duration. Originality/value According to the unique outcomes of this experimental study and, as the fire-damaged concrete columns possessed considerable residual compressive strength, in particular those exposed to shorter fire duration, it is anticipated that with proper retrofitting techniques such as fiber-reinforced polymers (FRP) wrapping, the fire-damaged columns can be rehabilitated to regain at least portion of its lost load-bearing capacities. Accordingly, the residual compressive resistance data obtained from this study can be effectively used but not directly to adopt optimal retrofitting strategies for such fire-damaged concrete columns, as well as to be used in validating numerical models that can be usefully used to account for the thermally-induced degradation of the mechanical properties of concrete material and ultimately predict the residual compressive strengths and deformations of concrete columns subjected to different load intensity ratios for various fire durations.

Sodium Exposure Tests on Limestone Concrete Used as Sacrificial Protection Layer in FBR

2006 ◽  
Author(s):  
F. C. Parida ◽  
S. K. Das ◽  
A. K. Sharma ◽  
P. M. Rao ◽  
S. S. Ramesh ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Concrete Block ◽  
Ultrasonic Pulse Velocity ◽  
Ultrasonic Pulse ◽  
Pulse Velocity ◽  
Hydrogen Gas ◽  
Test Duration ◽  
Structural Concrete ◽  
Rebound Hammer ◽  
Core Samples

Hot sodium coming in contact with structural concrete in case of sodium leak in FBR system cause damage as a result of thermo-chemical attack by burning sodium. In addition, release of free and bound water from concrete leads to generation of hydrogen gas, which is explosive in nature. Hence limestone concrete, as sacrificial layer on the structural concrete in FBR, needs to be qualified. Four concrete blocks of dimension 600mm × 600mm × 300mm with 300mm × 300mm × 150mm cavity were cast and subjected to controlled sodium exposure tests. They have composition of ordinary portland cement, water, fine and coarse aggregate of limestone in the ratio of 1 : 0.58 : 2.547 : 3.817. These blocks were subjected to preliminary inspection by ultrasonic pulse velocity technique and rebound hammer tests. Each block was exposed for 30 minutes to about 12 kg of liquid sodium (∼ 120 mm liquid column) at 550° C in open air, after which sodium was sucked back from the cavity of the concrete block into a sodium tank. On-line temperature monitoring was carried out at strategic locations of sodium pool and concrete block. After removing sodium from the cavity and cleaning the surfaces, rebound hammer testing was carried out on each concrete block at the same locations where data were taken earlier at pre-exposed stage. The statistical analysis of rebound hammer data revealed that one of the concrete block alone has undergone damage to the extent of 16%. The loss of mass occurred for all the four blocks varied from 0.6 to 2.4% due to release of water during the test duration. Chemical analysis of sodium in concrete samples collected from cavity floor of each block helped in generation of depth profiles of sodium monoxide concentration for each block. From this it is concluded that a bulk penetration of sodium up to 30 mm depth has taken place. However it was also observed that at few local spots, sodium penetrated into concrete up to 50 mm. Cylindrical core samples of 50 mm × 150 mm long were obtained from the exposed cavity and tested for compressive strength and longitudinal ultrasonic pulse velocity (UPV). These are compared with core samples obtained from concrete cubes used as standard reference. The average reduction in UPV and compressive strength were 7% and 29% respectively indicating marginal degradation in mechanical properties of sodium-exposed concrete.

STUDY OF REPLACEMENT OF SAND BY EXPANDED POLYSTYRENE IN STRUCTURAL LIGHTWEIGHT CONCRETE

2017 ◽  
Vol 4 (1) ◽  
Author(s):  
Mateus Titon Tostes ◽  
Daniel Hastenpflug
Keyword(s):  
Compressive Strength ◽  
Modulus Of Elasticity ◽  
Lightweight Concrete ◽  
Concrete Structures ◽  
Expanded Polystyrene ◽  
New Materials ◽  
Medium Sand ◽  
Structural Concrete

The search for more efficient concrete structures requires use of new materials in the developed of new concretes. With this objective, it was proposed in this study the substitution of Part of the medium sand of the lightweight structural concrete for expanded polystyrene (PS). It was replaced 5%, 10% and 20% of the sand to observe the changes in compressive strength, flowability, absorption, density and modulus of elasticity of these concretes. The results of the study show that there was an increase in the absorption and loss in the compressive strength and modulus of elasticity. Also, there was a significant increase in the flowability and reduction in the density of these concretes. Even with the replacement of part of the medium sand by expanded polystyrene, the concretes developed were classified as lightweight structural concretes, showing the applicability of this substitution in concrete designs.

Using lateritic gravel as all-in aggregate for concrete production

2017 ◽  
Vol 15 (03) ◽  
pp. 305-316 ◽  
Author(s):  
Richard Ohene Asiedu
Keyword(s):  
Compressive Strength ◽  
Design Methodology ◽  
Structural Concrete ◽  
Content Type ◽  
Rate Of Increase ◽  
Concrete Production ◽  
Alternative Sources ◽  
The Cost ◽  
Practical Implications ◽  
Better Than

Purpose The quest to reduce the cost of concrete which is a major construction input has prompted investigations into assessing the suitability of alternative sources of conventional materials. This paper aims to report the compressive strength and workability of lateritic gravel used as all-in aggregate for concrete production. Design/methodology/approach Three prescribed mixes from all-in aggregate concrete were compared with concrete from lateritic gravel. The paper investigated the variation in strength of four different mixes – 100: 0, 90: 10, 80: 20 and 70: 30 – when portions of the lateritic gravel were replaced with pit sand, respectively, using varying water cement ratios to achieve optimal workability. Findings The density and compressive strength of each cube was measured on the 7th and 28th test dates. An increase in slump and compressive strength was observed in the lateritic concrete, as portions of the lateritic gravel were replaced with sand. However, the rate of increase in the compressive strength tended to decrease with increase in part replacement of lateritic gravel with sand indicating that there was a threshold of percentage of sand increase after which the compressive strengths are likely to decrease. This work never reached this threshold, but it is estimated to be about 40 per cent. Research limitations/implications Investigations focused on lateritic gravel sampled from two sites to represent samples from both the forest and savannah belt. Practical/implications Lateritic gravel can be used as all-in aggregate for non-structural concrete. Originality/value The compressive strengths achieved were better than those for the available normal all-in aggregate used.

Diatomaceous earth aggregates based composite masonry blocks for bushfire resistance

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Indunil Erandi Ariyaratne ◽  
Anthony Ariyanayagam ◽  
Mahen Mahendran
Keyword(s):  
Compressive Strength ◽  
Fire Resistance ◽  
Residual Strength ◽  
Side Surface ◽  
Fire Exposure ◽  
Compression Tests ◽  
Content Type ◽  
Absolute Volume ◽  
Before And After ◽  
Volume Method

PurposeThis paper presents the details of a research study on developing composite masonry blocks using two types of mixes, conventional and lightweight mix, to enhance their fire/bushfire resistance and residual compressive strength.Design/methodology/approachComposite masonry blocks (390 × 190 × 90 mm) were fabricated using conventional cement–sand mix as the outer layer and lightweight cement–sand–diatomite mix as the inner layer. Material properties were determined, and all the mixes were proportioned by the absolute volume method. After 28 days of curing, density tests, compression tests before and after fire exposure and fire resistance tests of the developed blocks were conducted, and the results were compared with those of conventional cement–sand and cement–sand–diatomite blocks.FindingsDeveloped composite blocks satisfy density and compressive strength requirements for loadbearing lightweight solid masonry units. Fire resistance of the composite block is –/120/120, and no cracks appeared on the ambient side surface of the block after 3 h of fire exposure. Residual strength of the composite block is higher compared to cement–sand and cement–sand–diatomite blocks and satisfies the loadbearing solid masonry unit strength requirements.Practical implicationsComposite block developed in this research can be suggested as a suitable loadbearing lightweight solid masonry block for several applications in buildings in bushfire prone areas.Originality/valueLimited studies are available for composite masonry blocks in relation to their fire resistance and residual strength.

scholarly journals Mechanical and Thermal Properties of Geopolymers from Mixtures of Coal Ash and Rice Hull Ash using Water Glass Solution as Activator

2016 ◽  
Vol 15 (2) ◽  
pp. 51 ◽  
Author(s):  
Martin Ernesto L. Kalaw ◽  
Alvin B Culaba ◽  
Hoc Thang Nguyen ◽  
Khoi Nguyen ◽  
Hirofumi Hinode ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Compressive Strength ◽  
High Temperature ◽  
Mass Loss ◽  
Water Absorption ◽  
Residential Buildings ◽  
Coal Ash ◽  
Rice Hull ◽  
Rice Hull Ash ◽  
Temperature Exposure

Geopolymers, from industrial wastes such as blast furnace slag, red mud, and coal ash, among others, have emerged as technically viable, economically competitive, and environmentally attractive supplements and even alternatives to ordinary Portland cement (OPC). Furthermore, while the most impact shall be achieved with large-scale use in the general building and structural sector, as replacement or supplement to OPC, the properties of these geopolymers may be optimized for special niche applications. One of these applications is for light weight, low thermal conductivity, heat resistant, and moderate strength cement binder for low rise residential buildings. In this study, compressive strength, heat resistance, volumetric weight, mass loss, water absorption and thermal conductivity of geopolymers formed from mixtures of coal bottom ash and rice hull ash (CBA-RHA) and coal fly ash and rice hull ash (CFA-RHA) with sodium silicate solution (modulus 2.5) as activator were evaluated. Using mixture design and the JMP statistical software, the CBA-RHA combination at a mass ratio of 46% CBA, 32% RHA with 22% WGS gave properties at maximum desirability of 17.6 MPa compressive strength, 1640 kg/m3 volumetric weight, 273 kg/m3 water absorption, 28 MPa compressive strength after high temperature exposure (1000oC for 2 hours) with 4.4% mass loss, and 0.578 W/m-K thermal conductivity. On a performance basis, even as the geopolymers are formed as paste, these properties fall within the standards for lightweight OPC based-concrete with strength requirements for residential buildings. The low thermal conductivity and higher strength after high temperature exposure vis-à-vis OPC are additional advantages for consideration.

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