--- title: "Role of water; high water content" subject: "Concrete Technology and Masonry Structure" chapter: 1 key: "semester_5/concrete_technology_and_masonry_structure:water-high-content" source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/water-high-content site: BCT Engineering --- # Role of water; high water content Concrete Technology and Masonry Structure · Chapter 1: Introduction to concrete and concrete materials - Asked in: 2067 Magh (old course), 3+2 marks - Video: [Why Water-Cement Ratio Controls Concrete Strength](https://www.youtube.com/watch?v=_XnNoLfLQPQ) — Structural USB: Beyond the Blueprint - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/water-high-content - Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-1 ## Question What is the role of water in concrete? What are the advantages and drawbacks of use of high water content in concrete? ## Short answer Water hydrates cement, imparts workability, and enables curing. High water content improves workability and ease of placing and finishing. However, it sharply reduces strength (Abrams' law), increases porosity, permeability, bleeding, segregation, and drying shrinkage, harming durability and causing cracks. ## Answer #### Role of water Water hydrates the cement, gives workability by lubricating the particles and is required for curing. About 0.23 of the cement weight is chemically combined and 0.15 is physically held in the gel pores (total w/c of about 0.38 for full hydration); anything more only supplies workability. #### Advantages of high water content - Higher workability, easy mixing, placing and compaction, which helps in congested reinforcement and long pumping distances. - Easier finishing; lower labour effort. - Provides enough water for complete hydration and reduces plastic cracking in very dry mixes. #### Drawbacks - **Lower strength**: strength falls rapidly with w/c (Abrams' law, $f = A/B^{w/c}$). - Excess water leaves capillary pores on evaporation, so concrete is **more porous and permeable, less durable** (more chances of corrosion, frost and chemical attack). - Increases **bleeding and segregation**, laitance and a weak top surface; water pockets under aggregate and bars reduce bond. - Larger **drying shrinkage and creep**, causing cracks. - Longer setting time and higher formwork pressure. - Wastes cement when the cement is added to keep w/c constant. Workability should be increased with plasticisers, not extra water. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. About what w/c ratio is needed for full hydration (chemical plus gel water)? A. 0.15 B. 0.23 C. 0.38 D. 0.60 Answer: C. 0.23 is chemically combined and 0.15 is held in gel pores, totalling about 0.38. (Key point: Water for hydration) 2. According to Abrams' law, what happens to strength as w/c increases? A. It rises rapidly B. It falls rapidly C. It stays constant D. It rises then falls only after 28 days Answer: B. f = A/B^(w/c), so strength falls as w/c rises. (Key point: Strength vs w/c) 3. Why is high water content bad for durability? A. It lowers workability B. It reduces setting time C. It makes concrete denser D. Evaporating excess water leaves capillary pores, making concrete more porous and permeable Answer: D. Capillary pores raise permeability, allowing corrosion, frost and chemical attack. (Key point: Durability drawback) 4. What should be used to increase workability instead of extra water? A. More aggregate B. Plasticisers C. Finer sand only D. Less cement Answer: B. Plasticisers raise workability without raising w/c. 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