Concrete technology—selecting correct statements: Which of the following statements about concrete materials and joints are valid in standard practice?

Introduction / Context:

Concrete quality depends on correct proportioning of constituents and proper detailing. Several practical facts influence mix volume calculations and structural detailing decisions. This question groups common truths that technicians and engineers should remember on site and in design offices.

Given Data / Assumptions:

• Use of volumetric batching on small works where sand bulking matters.
• Awareness of moisture effects on fine aggregates.
• Provision of movement joints to control cracking in long members.
• Recognition that void reduction (denser packing) improves concrete strength.

Concept / Approach:

Bulking of sand occurs at intermediate moisture contents, increasing sand volume; it must be allowed for in volumetric proportioning to avoid under-sanding. Dry sand and fully saturated sand have nearly the same volume—bulking mainly appears between about 2–8% moisture. Concrete strength theory (e.g., gel–space ratio concepts) emphasizes minimizing voids for higher strength and durability. Movement joints (expansion/contraction) are introduced at practical spacing—often around 10–12 m or per code—to accommodate thermal/moisture movements and shrinkage.

Step-by-Step Solution:

Verification / Alternative check:

Site guides and codes of practice (e.g., IS/ACI) discuss bulking allowances, note negligible bulking at fully flooded condition, and recommend joint spacing limits to control cracking.

Why Other Options Are Wrong:

• Selecting any single statement ignores the validity of the others, while the question seeks the combined correct set.

Common Pitfalls:

• Failing to correct for bulking leads to lean mixes and poor workability.
• Omitting movement joints in long slabs and walls, leading to random cracking.

Final Answer:

All the above