Bulking and moisture in sand: Which statements are correct regarding causes, magnitude, and the saturated condition?

Introduction / Context:
Bulking affects batching by volume for mortars and concrete. If not accounted for, water and cement proportions become inaccurate, leading to weak mixes. Understanding how moisture changes apparent sand volume is a core construction management topic.

Given Data / Assumptions:

• Natural sand with varying grading from fine to coarse.
• Bulking arises at low to moderate moisture contents.
• At full saturation, water fills voids and surface tension effects vanish.

Concept / Approach:
(a) True: a surface moisture film causes grains to repel slightly due to menisci, increasing apparent volume. (b) True: fine sands have more surface area and smaller pores, so a given moisture content creates larger relative separation and thus greater bulking. (c) Not generally true: maximum bulking typically occurs around 4–6% moisture for fine sand, with volume increases often in the range of 20–35%, not as high as 50% at 10%. (d) True: at full saturation, meniscus forces vanish and the sand settles; the volume approaches that of dry loose sand.

Step-by-Step Solution:
Confirm cause → thin moisture film leads to apparent volume increase.Compare grading → finer sands bulk more.Evaluate 10% moisture claim → inconsistent with typical bulking curves; reject.Assess saturated condition → bulking disappears; volume ~ dry loose.Therefore, (a), (b), and (d) are correct together.

Verification / Alternative check:
Standard bulking charts show peak bulking at a few percent moisture, then decreasing toward zero at saturation.

Why Other Options Are Wrong:
Option including (c) is incorrect because the stated magnitude and moisture level are unrealistic for most sands.

Common Pitfalls:
Batching by volume without bulking correction; assuming constant bulking irrespective of grading.

Final Answer:
Only (a), (b), and (d) are correct.