--- title: "Physical causes of concrete deterioration" subject: "Concrete Technology and Masonry Structure" chapter: 6 key: "semester_5/concrete_technology_and_masonry_structure:physical-causes-deterioration" source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/physical-causes-deterioration site: BCT Engineering --- # Physical causes of concrete deterioration Concrete Technology and Masonry Structure · Chapter 6: Concrete durability - Asked in: 2080 Bhadra, 3 marks; 2075 Chaitra, 6 marks; 2074 Chaitra, 6 marks; 2067 Magh (old course), 2+3 marks; 2066 Chaitra (old course), 5 marks (asked 5 times) - Video: [Deterioration of Concrete Structures: Part 1](https://www.youtube.com/watch?v=wjH6OtBbbW8) — Curious Civil Engineer - Answer checked by Claude Sonnet 5.5 on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/physical-causes-deterioration - Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-6 ## Question Explain the physical causes of concrete deterioration. ## Short answer Physical causes include freezing-thawing (water expansion causing scaling/cracking), thermal effects (differential expansion, fire spalling), shrinkage cracking, abrasion, erosion/cavitation, salt crystallization, and wetting-drying cycles. All increase permeability; control by low w/c, air entrainment, and good curing. ## Answer Physical causes act by mechanical, thermal or moisture processes without changing the chemical composition of cement paste. | 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. 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) 2. What happens to cement paste at high temperature in a fire? A. It gains strength because more hydration occurs B. Above 300 °C paste loses water and above 500 °C Ca(OH)2 decomposes, causing cracking, spalling and strength loss C. Only the aggregate is affected D. Ca(OH)2 forms above 500 °C Answer: B. Dehydration and decomposition of Ca(OH)2 weaken the paste. (Key point: Thermal and fire effects) 3. 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) 4. What is the general effect of physical processes on later chemical attack? A. They make concrete denser and slow chemical attack B. They have no link to chemical attack C. They only affect colour D. They increase permeability and speed up chemical attack Answer: D. Cracks and scaling open paths for water and ions; low w/c, curing and compaction help. (Key point: Physical causes and permeability) ## Close variants set in other exams - [Mechanical and physical causes of deterioration](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Amechanical-physical-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×