--- title: "Mechanical and physical causes of deterioration" subject: "Concrete Technology and Masonry Structure" chapter: 6 key: "semester_5/concrete_technology_and_masonry_structure:mechanical-physical-causes-deterioration" source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/mechanical-physical-causes-deterioration site: BCT Engineering --- # Mechanical and physical causes of deterioration Concrete Technology and Masonry Structure · Chapter 6: Concrete durability - Asked in: 2075 Ashwin, 4+3 marks - Video: [Factors causing deterioration](https://www.youtube.com/watch?v=t6Ytyw8dMQo) — Tech Guru - Answer checked by Claude Sonnet 5.5 on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/mechanical-physical-causes-deterioration - Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-6 ## Question Describe the mechanical and physical causes of concrete deterioration. ## Short answer Mechanical causes include overloading, impact, vibration, settlement, and abrasion. Physical causes are freeze-thaw cycles, thermal effects, drying shrinkage, salt crystallization, and wetting/drying, all of which increase permeability and accelerate chemical attack. ## Answer #### Mechanical causes Mechanical causes are those from applied loads and impacts: - **Overloading** and structural defects, causing cracks beyond design level. - **Impact** (vehicle collision, pile driving, falling objects), **vibration** and fatigue from machinery or traffic, causing cracks and spalling. - **Settlement** and movement of supports, and earthquakes. - **Abrasion and erosion** by traffic, water flow with silt and cavitation, which wear the surface. - **Explosion**, blasting. Control: correct design for loads, joints, stiff foundations, hard aggregate and high strength for wearing surfaces. #### Physical causes | Cause | Mechanism | Effect and control | |---|---|---| | **Freezing and thawing** | Water in pores freezes, expanding by 9%, causing hydraulic pressure; repeated cycles | Scaling, cracking, D-cracking. Use air entrainment (4 to 7%), low w/c, sound aggregate | | **Thermal effects** (temperature cycle, fire) | Differential expansion/contraction; above 300 °C paste loses water, above 500 °C Ca(OH)2 decomposes | Cracking, spalling, loss of strength. Joints, cover, insulation | | **Shrinkage and moisture movement** | Drying shrinkage restrained by steel/supports | Cracks, which open the way for aggressive agents. Low w/c, curing, joints | | **Abrasion** | Wear by traffic, sliding or rolling | Surface loss in pavements, floors. Hard aggregates, high strength, surface treatments | | **Erosion and cavitation** | High velocity water with silt, or vapour bubbles collapsing | Pitting of spillways. Smooth surface, high-strength concrete | | **Salt crystallisation** | Salt solution crystallises in pores on drying | Pressure causing scaling and efflorescence. Dense concrete, membranes | | **Wetting and drying** | Moisture gradients cause cyclic stress | Cracking and surface deterioration | All physical processes increase permeability and speed up chemical attack, so low w/c, good curing and compaction help in all of them. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which is a mechanical cause of concrete deterioration? A. Sulphate attack B. Overloading, impact, vibration/fatigue, settlement, earthquakes, explosion C. Carbonation D. Alkali-silica reaction Answer: B. Mechanical causes arise from loads and impacts, unlike chemical causes. (Key point: Mechanical causes) 2. What control applies to mechanical deterioration? A. Using high w/c concrete B. Avoiding joints C. Correct design for loads, joints, stiff foundations, and hard aggregate and high strength for wearing surfaces D. Using soft aggregates Answer: C. Design and material choices reduce cracking and wear. (Key point: Mechanical control) 3. How does freezing and thawing damage concrete? A. Ice contracts and pulls the paste apart B. Frozen water reacts with C3A to form ettringite C. Freezing dissolves Ca(OH)2 which leaches out D. Water in pores expands about 9% on freezing, creating hydraulic pressure; repeated cycles crack and scale it Answer: D. The 9% expansion of freezing pore water causes pressure; control by air entrainment (4 to 7%) and low w/c. (Key point: Freeze-thaw mechanism) 4. Why does drying shrinkage cause cracks? A. Concrete expands on drying and crushes B. Shrinkage only occurs when concrete freezes C. Shrinkage is restrained by steel or supports, producing tensile stress; the cracks let aggressive agents in D. Shrinkage is caused by sulphates Answer: C. Restraint turns shrinkage into tension; control by low w/c, curing and joints. (Key point: Shrinkage cracking) ## Close variants set in other exams - [Physical causes of concrete deterioration](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aphysical-causes-deterioration) — Concrete Technology and Masonry Structure, chapter 6, asked 6× ## Related in Concrete Technology and Masonry Structure - [Physical and chemical causes of deterioration](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aphysical-chemical-causes-deterioration) — Concrete Technology and Masonry Structure, chapter 6, asked 5× - [Chemical causes of concrete deterioration](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Achemical-causes-deterioration) — Concrete Technology and Masonry Structure, chapter 6, asked 5× - [Causes of deterioration; effects of steel corrosion](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Acauses-deterioration-corrosion-effects) — Concrete Technology and Masonry Structure, chapter 6, asked 2× - [Physical properties of OPC and concrete behaviour](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Acement-physical-properties) — Concrete Technology and Masonry Structure, chapter 1 ## Related in other subjects - [Causes of deterioration of stone](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Acauses-deterioration-stone) — Civil Engineering Materials, chapter 2, asked 4× - [Physical and mechanical properties of wood](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Aphysical-mechanical-properties-wood) — Civil Engineering Materials, chapter 7