By the end of this chapter, you will be able to:
Mastering these skills will help you choose the right materials for any construction project and ensure your work meets professional standards.
Physical properties determine how construction materials behave under various conditions and affect their suitability for specific applications in the built environment. Kenyan quantity surveyors must assess these properties to ensure materials meet project specifications, avoid wastage, and uphold structural integrity.
Porosity refers to the volume fraction of void spaces within a material, influencing its ability to absorb and transmit fluids, gases, or moisture. It is a critical consideration in materials like concrete, bricks, and timber used in Kenya’s humid coastal regions or highland areas prone to heavy rainfall.
Porosity measures the ratio of the volume of pores or voids to the total volume of a material. High porosity implies more void spaces, which can lead to greater water absorption and reduced strength. For example, porous bricks used in Nairobi’s construction may absorb moisture, affecting wall durability.
Materials with high porosity tend to be weaker and less durable because absorbed water can cause swelling, frost damage, or corrosion of embedded metals. In the case of concrete used in counties like Kisumu, excessive porosity can lead to faster degradation under wet conditions.
Porous materials often provide better insulation by trapping air in voids, reducing heat transfer and noise. This characteristic is beneficial in schools or hospitals where thermal comfort and noise reduction are priorities.
Porosity is commonly tested by measuring water absorption or using methods like mercury intrusion porosimetry in laboratories. Quantity surveyors can interpret test results to verify supplier claims and ensure compliance with standards such as Kenya Standards (KS) for building materials.
The surface properties of construction materials affect their appearance, bonding with other materials, and resistance to environmental factors. Quantity surveyors must consider surface characteristics when specifying finishes or evaluating material suitability for external or internal applications.
Surface texture refers to the roughness or smoothness of a material’s exterior. Rough surfaces, such as those of unpolished stone or coarse concrete, provide better mechanical bonding with plaster or mortar, essential in masonry work for county government offices.
Surface porosity impacts how materials absorb paints, sealants, and adhesives. For example, porous concrete blocks in hotel construction may require surface treatment to prevent premature paint peeling caused by moisture ingress.
Materials with hard surfaces resist scratches and wear, maintaining aesthetic appeal and structural integrity. Floor tiles in retail businesses must have surfaces that withstand foot traffic without significant damage.
The chemical nature of a surface can affect durability. Materials like limestone may react with acidic rain, common in Nairobi’s industrial areas, leading to surface erosion and necessitating protective coatings.
Texture describes the feel and appearance of a material’s surface, influenced by grain size, shape, and arrangement. It affects workmanship quality, aesthetic value, and material handling during construction.
Fine-grained materials such as smooth cement render provide a polished finish, while coarse aggregates create rough textures that improve mechanical interlocking in concrete mixes. Quantity surveyors must understand texture when estimating material quantities for finishes.
Texture affects how easily materials can be manipulated. Smooth textures facilitate plaster application in hospitals, whereas rough textures may require more effort but improve adhesion.
Texture contributes to the architectural expression of buildings. For instance, textured stone cladding in university buildings offers aesthetic variation and a sense of solidity.
Coarse textures often indicate stronger materials due to larger aggregate sizes, but may also be more brittle. Understanding this balance is important when specifying materials for different structural elements.
Strength is the capacity of a material to withstand applied forces without failure. It is a paramount property in ensuring safety and longevity of structures, directly influencing cost estimation and risk management.
Compressive strength measures resistance to crushing forces, critical for materials like concrete and bricks supporting loads in buildings. For example, concrete used in Nairobi County offices must meet minimum compressive strength to comply with building codes.
Tensile strength is the ability to resist pulling forces. Steel reinforcement bars used in reinforced concrete slabs in hospitals require high tensile strength to prevent cracking.
Flexural strength indicates resistance to bending forces, important for beams and slabs subject to dynamic loads in retail malls or schools.
Shear strength measures the capacity to resist sliding forces between material layers, essential in masonry walls subjected to lateral wind loads in coastal regions.
Impact strength reflects the ability to absorb sudden shocks without fracturing. Materials used in public transport terminals must have good impact resistance to withstand accidental collisions.
Density is the mass per unit volume of a material, influencing structural load, transport costs, and thermal properties. Quantity surveyors must consider density when calculating material quantities and assessing structural design implications.
Density is expressed in kilograms per cubic meter (kg/m³). For example, normal concrete density ranges from 2200 to 2500 kg/m³, affecting the dead load in multi-storey buildings in Nairobi.
Higher density materials increase the weight of a structure, impacting foundation design and cost. Lightweight concrete blocks reduce load and may be preferred in hospital expansions with weak soils.
Dense materials cost more to transport due to weight, influencing the overall project budget. For county government projects in remote areas, selecting materials with optimal density can reduce logistics expenses.
Generally, higher density correlates with lower porosity and greater strength, but exceptions exist. Understanding these relationships aids quantity surveyors in material selection and specification.
Thermal conductivity measures a material’s ability to conduct heat, affecting energy efficiency and occupant comfort. In Kenya’s varying climates, selection of materials with appropriate thermal properties is vital for sustainable construction.
Thermal conductivity is expressed in watts per meter-kelvin (W/m·K). Materials like clay bricks have moderate conductivity, balancing heat retention and dissipation in residential buildings.
Materials with low thermal conductivity provide better insulation, reducing cooling or heating costs. Hospitals in arid regions benefit from walls constructed with insulating materials to maintain stable indoor temperatures.
Quantity surveyors must consider thermal conductivity when specifying wall and roofing materials to meet green building standards and client requirements.
Appropriate thermal properties contribute to thermal comfort, enhancing occupant wellbeing. Schools designed with insulating materials reduce reliance on mechanical ventilation.
Wear and tear describes the gradual deterioration of materials under mechanical action or environmental exposure. Assessing this property guides maintenance planning and lifecycle costing.
Wear results from friction, abrasion, chemical attack, or weathering. For example, floor finishes in busy retail outlets experience accelerated wear due to foot traffic.
Materials with high abrasion resistance maintain surface integrity longer, reducing replacement frequency. Granite countertops in hotel kitchens exemplify durable surfaces.
Exposure to UV radiation, rain, or pollution causes material breakdown. External paints on county buildings require protective formulations to withstand Nairobi’s climatic conditions.
Understanding wear patterns helps quantity surveyors plan maintenance budgets and schedules, ensuring asset longevity and cost control.
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Create a free accountThis chapter explored the essential properties of construction materials, beginning with physical characteristics such as porosity, surface quality, texture, strength, density, thermal conductivity, and resistance to wear and tear. Each physical property influences how materials perform in different construction environments and applications. The discussion then moved to chemical properties, focusing on corrosion resistance and chemical resistance, which determine a material's durability when exposed to various chemical environments. Mechanical properties were also examined in depth, including toughness, hardness, fatigue, and the behavior of materials under stress and strain. Additionally, the chapter covered creep and stress rupture, highlighting how materials deform over time under constant load. The concept of strength was revisited in the mechanical context, emphasizing its critical role in ensuring structural integrity. Overall, understanding these properties is fundamental for selecting appropriate materials that meet the demands of safety, durability, and functionality in construction projects.
Type: Individual
| Tools & Equipment | Materials |
|---|---|
| Digital Weighing Scale (capacity 5kg, accuracy 1g) | Water (clean, distilled) |
| Vernier Caliper (0-150mm) | Samples of construction materials (concrete, brick, timber) |
| Measuring Cylinder (500 ml) | |
| Beaker (1000 ml) | |
| Porosity Test Jar (airtight, 1 litre capacity) | |
| Sandpaper (medium grit) |
| S/N | Item | Quantity |
|---|---|---|
| 1 | Digital Weighing Scale (capacity 5kg, accuracy 1g) | 1 Pc per Candidate |
| 2 | Vernier Caliper (0-150mm) | 1 Pc per Candidate |
| 3 | Measuring Cylinder (500 ml) | 1 Pc per Candidate |
| 4 | Beaker (1000 ml) | 1 Pc per Candidate |
| 5 | Water (clean, distilled) | Sufficient per Candidate |
| 6 | Porosity Test Jar (airtight, 1 litre capacity) | 1 Pc per Candidate |
| 7 | Sandpaper (medium grit) | 1 Pc per Candidate |
| 8 | Safety Gloves | 1 Pair per Candidate |
| 9 | Safety Goggles | 1 Pc per Candidate |
| 10 | Notebook and Pen | 1 Set per Candidate |
| 11 | Samples of construction materials (concrete, brick, timber) | 3 Samples per Candidate |
| Items to be Evaluated | Marks Available | Marks Obtained | Comments |
|---|---|---|---|
| TASK 1: SAMPLE PREPARATION AND PPE | |||
| Identified and correctly donned safety gloves and goggles (Award 1 mark each for gloves and goggles) | 2 | ||
| Cleaned and prepared material samples (e.g. smoothing surfaces with sandpaper) (Award 2 marks for proper preparation of all samples) | 2 | ||
| Assembled all tools and materials needed for the tests (Award 1 mark for correct assembly) | 1 | ||
| Sub-Total | 5 | ||
| TASK 2: DETERMINATION OF DENSITY | |||
| Measured and recorded the mass of each material sample accurately using the digital scale (Award 1 mark for each correct mass measurement) | 3 | ||
| Measured dimensions of each sample using vernier caliper and calculated volume correctly (Award 1 mark per sample for correct volume measurement and calculation) | 3 | ||
| Calculated and recorded density of each sample correctly (Award 1 mark per sample for correct density calculation) | 3 | ||
| Sub-Total | 9 | ||
| TASK 3: DETERMINATION OF POROSITY | |||
| Filled porosity test jar with water and recorded initial volume (Award 1 mark for correct initial volume reading) | 1 | ||
| Submerged each sample in water and recorded volume displacement accurately (Award 1 mark per sample for correct volume displacement reading) | 3 | ||
| Calculated porosity (%) for each sample using volume and mass data (Award 1 mark per sample for correct porosity calculation) | 3 | ||
| Sub-Total | 7 | ||
| TASK 4: RECORDING AND CLEAN-UP | |||
| Recorded all data neatly and accurately in the notebook (Award 2 marks for complete and legible records) | 2 | ||
| Cleaned and stored all tools and materials properly after use (Award 2 marks for proper cleaning and storage) | 2 | ||
| Sub-Total | 4 | ||
| PRODUCT CHECKLIST | |||
| Accurate density values for all three samples within ±5% tolerance of standard values (Award 2 marks per sample for correct density within tolerance) | 6 | ||
| Accurate porosity values for all three samples within ±5% tolerance of standard values (Award 2 marks per sample for correct porosity within tolerance) | 6 | ||
| Complete and well-organized record sheet with all measurements and calculations (Award 4 marks for complete and clear documentation) | 4 | ||
| Sub-Total | 16 | ||
| GRAND TOTAL | 41 | ||
Type: Individual
| Tools & Equipment | Materials |
|---|---|
| Magnifying glass (10x) | Concrete block 200mm x 100mm |
| Surface roughness comparator plates | Timber plank 1000mm x 150mm |
| Steel trowel | Mild steel sheet 300mm x 300mm |
| Sandpaper (various grits 80, 120, 220) | Ceramic tile 200mm x 200mm |
| Cloth rag | |
| Safety gloves | |
| Safety goggles |
| S/N | Item | Quantity |
|---|---|---|
| 1 | Magnifying glass (10x) | 1 Pc per Candidate |
| 2 | Surface roughness comparator plates | 1 Set per 2 Candidates |
| 3 | Steel trowel | 1 Pc per Candidate |
| 4 | Sandpaper (various grits 80, 120, 220) | 3 Sheets per Candidate |
| 5 | Cloth rag | 1 Pc per Candidate |
| 6 | Safety gloves | 1 Pair per Candidate |
| 7 | Safety goggles | 1 Pair per Candidate |
| 8 | Samples of construction materials (concrete block, timber plank, mild steel sheet, ceramic tile) | 1 Set per Candidate |
| 9 | Notebook and pen | 1 Set per Candidate |
| Items to be Evaluated | Marks Available | Marks Obtained | Comments |
|---|---|---|---|
| TASK 1: PREPARATION AND SAFETY | |||
| Candidate dons safety gloves and safety goggles correctly (Award 1 mark each for correctly worn gloves and goggles) | 2 | ||
| Candidate assembles all required tools and material samples before starting (Award 2 marks for complete assembly of tools and materials) | 2 | ||
| Candidate prepares the working surface and organizes samples in an accessible manner (Award 1 mark for neat and safe preparation of workspace) | 1 | ||
| Sub-Total | 5 | ||
| TASK 2: SURFACE EXAMINATION | |||
| Candidate visually inspects surface texture of each material using magnifying glass (Award 1 mark for each material correctly examined visually using magnifying glass) | 4 | ||
| Candidate uses tactile method (touch and steel trowel) to assess roughness and finish of each material (Award 1 mark for each material tactilely examined with appropriate tools) | 4 | ||
| Candidate compares surface texture using roughness comparator plates and identifies texture grades (Award 1 mark for each correctly identified texture grade for three materials) | 3 | ||
| Candidate cleans samples after examination using cloth rag (Award 1 mark for cleaning samples properly) | 1 | ||
| Sub-Total | 12 | ||
| TASK 3: RECORDING AND REPORTING | |||
| Candidate records observations clearly and accurately in the notebook (Award 1 mark for each material's surface description clearly recorded) | 3 | ||
| Candidate summarizes findings with appropriate terminology related to surface texture and finish (Award 3 marks for clear, accurate summary using correct technical terms) | 3 | ||
| Candidate cleans and stores tools and materials properly after task completion (Award 2 marks for correct cleaning and storage) | 2 | ||
| Sub-Total | 8 | ||
| PRODUCT CHECKLIST | |||
| Surface texture descriptions match observed tactile and visual characteristics for all four materials (Award 1.5 marks for each material's accurate surface texture description) | 6 | ||
| Surface finish assessment includes correct identification of smoothness, roughness, or other relevant finish qualities (Award 4 marks for accurate finish characterization across all materials) | 4 | ||
| Sub-Total | 10 | ||
| GRAND TOTAL | 35 | ||
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