Fire Resistance of Locally Sourced Construction Materials
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Abstract
About This Research Topic
Walk onto almost any Nigerian building site and you'll see the same handful of walling materials going up: sandcrete blocks, compressed stabilised earth blocks, or, less commonly now, fired clay bricks. What you won't usually see is any evidence of how these materials actually perform when a fire breaks out. Fire safety testing is routine in more developed construction markets, but for materials produced and used the way they are in Nigeria, standardised fire performance data has been surprisingly thin on the ground.
This article draws on a laboratory study that put all three materials through the same standardised fire test, exposing wall panels and cube specimens to increasing durations of controlled heat and measuring exactly how much strength each material lost, how hot the unexposed face got, and whether the material cracked or spalled under pressure. For readers curious how a study like this is designed and run, our sample research projects library includes comparable materials science and civil engineering studies worth reviewing as models.
The results carry real weight for anyone specifying walling materials for buildings where fire risk is a serious design consideration, hospitals, schools, high-rise residential blocks, and public buildings among them. The sections below walk through the background to the problem, what the study actually did, and what its findings mean for materials selection in Nigerian construction.
Main Abstract
Fire safety is a critical performance requirement for building materials, yet it's one that's often overlooked in Nigeria, where locally produced walling materials, sandcrete blocks, compressed stabilised earth blocks, and fired clay bricks, are used widely without much empirical verification of how they actually perform under standardised fire conditions. This study evaluated the fire resistance of three locally sourced walling materials, sandcrete hollow blocks (a 1:6 cement-sand mix), compressed stabilised earth blocks (laterite stabilised with 6 percent cement), and traditional fired clay bricks, by exposing them to the internationally recognised ISO 834 standard time-temperature fire curve in a laboratory furnace, at exposure durations of 30, 60, 90, and 120 minutes.
For each material and exposure duration, the study measured unexposed face temperature rise, residual compressive strength, mass loss, and visual damage such as cracking and spalling, using 150 mm thick wall panels for insulation testing and companion 100 mm cube specimens for strength testing.
All three materials met the insulation criterion, meaning unexposed face temperature rise stayed below 140°C, at every exposure duration tested up to 120 minutes. Compressed stabilised earth blocks performed best on this measure, recording a temperature rise of just 62°C at 60 minutes thanks to the material's comparatively low thermal conductivity, against 98°C for sandcrete blocks and 85°C for fired clay bricks.
On residual compressive strength after 120 minutes of exposure, fired clay bricks came out ahead, retaining 76 percent of their original strength, followed by compressed stabilised earth blocks at 60 percent, with sandcrete blocks trailing at just 41 percent. Sandcrete blocks also showed visible surface spalling beyond 90 minutes of exposure, a result of calcium hydroxide breaking down under heat and differential thermal expansion between the cement paste and aggregate. Statistical testing confirmed that the strength differences among the three materials at 90 minutes were highly significant, and strong, near-linear relationships held between exposure duration and strength retention for all three materials.
The study concludes that fired clay bricks offer the best fire resistance among the three materials tested, followed by compressed stabilised earth blocks, with conventional sandcrete blocks performing the worst, differences that trace back to how each material's binding chemistry holds up under heat. It recommends that fire-rated wall specifications for high fire-risk building occupancies in Nigeria give real consideration to walling material choice, favouring fired clay brick or compressed stabilised earth block construction over conventional sandcrete blockwork wherever fire resistance is a genuine design priority.
Chapter One Preview
Background to the Study
Fire safety ranks among the most critical performance requirements for any building material, given how catastrophic structural or compartmental failure during a fire can be, both for life safety and for property. In more developed construction markets, rigorous, standardised fire resistance testing is a routine part of approving materials and building systems. That same rigour has been comparatively rare for many of the locally produced walling materials that dominate Nigerian construction, sandcrete blocks, compressed stabilised earth blocks, and traditional fired clay bricks, despite how widely these materials are relied on across residential, commercial, and institutional buildings nationwide.
Sandcrete blocks, made from a cement-sand mixture, dominate contemporary Nigerian urban construction, prized for consistent quality control, ready availability, and ease of use with conventional building practice, and the Standards Organisation of Nigeria maintains specific standards governing their manufacture and use. Compressed stabilised earth blocks, made from laterite soil stabilised with a modest amount of cement and compacted under mechanical pressure, represent a more traditional, lower-embodied-energy walling material that's seeing renewed interest as a sustainable alternative. Fired clay bricks, produced by firing moulded clay at high kiln temperatures, are one of the oldest walling technologies still in limited use in Nigeria, particularly in regions with strong local brick-making traditions. Each material's distinct thermal and mechanical properties, shaped by its constituent materials and manufacturing process, would be expected to produce different fire performance, yet comparative, standardised empirical data on this within the Nigerian material context has remained scarce.
This study set out to investigate the comparative fire resistance of these three locally sourced walling materials by exposing them to the ISO 834 standard time-temperature fire curve, the internationally recognised benchmark for fire resistance testing, inside a laboratory fire testing furnace. It assessed insulation performance through unexposed face temperature rise, residual mechanical performance through compressive strength retention after fire exposure and cooling, mass loss, and visual damage, with the goal of generating empirically grounded, comparative fire performance data to guide materials selection for fire-rated building applications in the Nigerian construction context.
Statement of the Problem
Nigerian building design and construction practice frequently proceeds with limited explicit consideration of how locally available walling materials actually perform in a fire, in part because standardised, empirically rigorous fire testing data specific to materials such as sandcrete blocks, compressed stabilised earth blocks, and fired clay bricks, as produced and used in Nigeria, has been scarce. This gap in locally grounded fire performance data limits the ability of architects, structural engineers, and building control authorities to make informed, evidence-based materials selection decisions for building occupancies where fire resistance is a particularly critical design consideration, high-occupancy public buildings, healthcare facilities, and high-rise residential developments among them.
This study addresses that gap through a rigorous, standardised comparative fire resistance evaluation of three prevalent locally sourced walling materials, generating quantified performance data to inform materials selection and fire safety design decisions in Nigerian construction practice.
Aim and Objectives of the Study
The aim of this study is to evaluate the comparative fire resistance performance of three locally sourced construction walling materials: sandcrete hollow blocks, compressed stabilised earth blocks, and fired clay bricks.
The specific objectives of the study are to:
● Determine the physical and mechanical properties of the three materials under unheated (ambient) conditions.
● Expose wall panel and cube specimens of each material to the ISO 834 standard time-temperature fire curve at exposure durations of 30, 60, 90 and 120 minutes.
● Determine the unexposed face temperature rise of each material at each exposure duration, to assess compliance with the insulation criterion.
● Determine the residual compressive strength of each material following fire exposure and subsequent cooling, at each exposure duration.
● Determine the mass loss of each material at each exposure duration.
● Assess and document the visual damage (cracking, spalling) exhibited by each material at each exposure duration.
● Establish the statistical relationship between exposure duration and residual strength retention for each material, and determine whether the observed differences among the three materials are statistically significant.
Research Questions
This study seeks to answer the following research questions:
● What are the physical and mechanical properties of sandcrete blocks, compressed stabilised earth blocks, and fired clay bricks under unheated conditions?
● How does unexposed face temperature rise vary among the three materials at increasing exposure durations, and do all three materials satisfy the insulation criterion?
● How does residual compressive strength vary among the three materials at increasing exposure durations?
● How does mass loss vary among the three materials at increasing exposure durations?
● What visual damage characteristics (cracking, spalling) are exhibited by each material at increasing exposure durations?
● Is there a statistically significant difference in residual strength retention among the three materials, and what is the statistical relationship between exposure duration and strength retention for each material?
Justification/Significance of the Study
This study is significant in several respects. It generates rigorous, standardised comparative fire performance data for three prevalent locally sourced walling materials, addressing a notable gap given how scarce this kind of empirically grounded data has been for materials as actually produced and used within the Nigerian construction context.
The findings offer direct practical value to architects, structural engineers, building control authorities, and developers looking for evidence-based guidance on walling material selection in fire-critical building applications, particularly given the clear performance differences identified among the three materials. Students and early-career researchers working on similar materials testing, comparative statistical analysis, or building performance studies can get direct feedback on study design and methodology through our research coaching service, and explore related technical studies in our civil engineering project archive.
The study also contributes to the broader academic literature on the fire performance of alternative and traditional walling materials, offering a rigorous, standardised comparative methodology that could be extended to other locally available construction materials in future research. More broadly, it supports better building fire safety outcomes in Nigeria by giving built environment professionals quantified, comparative fire performance data to inform more evidence-based, risk-appropriate materials selection.
Scope of the Study
This study is limited to the comparative fire resistance evaluation of three locally sourced walling materials: sandcrete hollow blocks (cement-sand, 1:6 mix), compressed stabilised earth blocks (laterite stabilised with 6 percent cement), and fired clay bricks, at a uniform wall panel thickness of 150 mm, exposed to the ISO 834 standard time-temperature fire curve for durations of 30, 60, 90, and 120 minutes. It covers unexposed face temperature rise for insulation criterion assessment, residual compressive strength, mass loss, and visual damage assessment.
The study does not extend to full-scale, load-bearing fire resistance testing under the integrity and load-bearing capacity criteria typically assessed in comprehensive structural fire testing (BS 476 Part 21/22 or equivalent), nor does it examine the fire performance of these materials within a complete wall assembly incorporating plaster finishes, both recommended for further research.
Operational Definition of Terms
Fire Resistance: The ability of a building material or element to withstand exposure to fire for a specified period while maintaining its load-bearing capacity, integrity, and insulation performance, as applicable to its intended function.
Insulation Criterion: A fire resistance performance requirement stipulating that the temperature rise on the unexposed face of a fire-separating element must not exceed a specified limit (commonly 140°C average rise, or 180°C maximum rise at any point) during the standard fire exposure period, to prevent ignition of combustible materials on the unexposed side.
ISO 834 Standard Time-Temperature Curve: An internationally recognised, standardised furnace temperature-time relationship used in fire resistance testing, designed to represent a fully developed compartment fire for testing and rating purposes.
Residual Compressive Strength: The compressive strength of a material remaining after exposure to elevated temperature and subsequent cooling, typically expressed as a percentage of the material's original (unheated) compressive strength.
Spalling: The violent or progressive breaking away of surface material from a heated element, typically arising from internal pore pressure build-up (in moisture-containing materials) or differential thermal expansion between constituent materials.
Compressed Stabilised Earth Block (CSEB): A masonry unit produced by compacting a mixture of soil (typically laterite) and a stabilising agent (commonly a modest proportion of cement or lime) under mechanical pressure, without firing.
Conclusion
When it comes to fire performance, not all Nigerian walling materials are created equal. Fired clay bricks held onto more of their strength after two hours of standardised fire exposure than either compressed stabilised earth blocks or conventional sandcrete blocks, and sandcrete's tendency to spall under sustained heat is a real, measurable risk rather than just a theoretical concern. For anyone specifying walling materials for a fire-critical building, the practical takeaway is clear: material choice deserves as much attention as structural design when fire resistance genuinely matters. Readers interested in related materials science and structural engineering research can browse more civil engineering project topics for further reading.
Frequently Asked Questions (FAQs)
Which locally sourced walling material has the best fire resistance in Nigeria?
Among the three materials tested, fired clay bricks performed best, retaining 76 percent of their original compressive strength after 120 minutes of standardised fire exposure, ahead of compressed stabilised earth blocks (60 percent) and sandcrete blocks (41 percent).
Do sandcrete blocks perform well in a fire?
Not as well as the alternatives tested. Sandcrete blocks retained only 41 percent of their original compressive strength after 120 minutes of fire exposure and showed visible surface spalling beyond 90 minutes, caused by the breakdown of calcium hydroxide and differential thermal expansion between the cement paste and aggregate.
What is the insulation criterion in fire resistance testing?
The insulation criterion requires that the temperature rise on the unexposed face of a fire-separating element stay below a set limit, commonly 140°C average rise, during the standard fire exposure period, to prevent materials on the other side from igniting.
Did all three materials meet the insulation criterion in this study?
Yes. Sandcrete blocks, compressed stabilised earth blocks, and fired clay bricks all kept unexposed face temperature rise below 140°C at every exposure duration tested, up to 120 minutes, though compressed stabilised earth blocks performed best on this specific measure.
What is the ISO 834 fire curve, and why is it used in testing?
ISO 834 is an internationally recognised standard time-temperature curve used in fire resistance testing to represent a fully developed compartment fire, allowing materials and building elements to be tested and rated on a consistent, comparable basis.
Why do compressed stabilised earth blocks resist heat transfer so well?
Compressed stabilised earth blocks recorded the lowest unexposed face temperature rise of the three materials, just 62°C at 60 minutes, attributable to the comparatively low thermal conductivity of the stabilised earth material compared to sandcrete or fired clay.
What is spalling, and why does it matter for fire safety?
Spalling is the violent or progressive breaking away of surface material from a heated element, often caused by internal pore pressure or differential thermal expansion. In this study, sandcrete blocks showed visible spalling beyond 90 minutes of fire exposure, a sign of accelerating structural weakness under sustained heat.
Should sandcrete blocks be avoided in fire-critical buildings?
The study recommends that fire-rated wall specifications for high fire-risk building occupancies in Nigeria give explicit consideration to walling material selection, favouring fired clay brick or compressed stabilised earth block construction over conventional sandcrete blockwork where enhanced fire resistance is a genuine design priority.
What building types should prioritise fire-resistant walling materials?
High fire-risk occupancies such as high-occupancy public buildings, healthcare facilities, and high-rise residential developments are where walling material fire performance matters most, and where evidence-based material selection carries the greatest safety benefit.
How was residual compressive strength measured in this study?
Companion 100 mm cube specimens of each material were exposed to the ISO 834 fire curve for set durations, allowed to cool, and then tested for compressive strength, expressed as a percentage of the material's original, unheated strength.
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