Mortar technology: why is sand added to cement mortar? Choose the correct set of reasons from the options provided.

Introduction / Context:
Sand (fine aggregate) is a fundamental component of mortar. Its roles include improving workability, controlling shrinkage, and reducing cost by lowering cement content. Understanding the true benefits (and limits) avoids common misconceptions about strength.

Given Data / Assumptions:

• (1) Decreasing the quantity of cement (economy).
• (2) Reducing shrinkage.
• (3) Decreasing the effective surface area of binding material by volumetric replacement.
• (4) Increasing the strength.

Concept / Approach:
Adding sand reduces paste content, which reduces drying shrinkage and thermal cracking. It also cuts cost by substituting a cheaper filler for expensive cement. While an appropriately graded sand improves packing and can optimize strength for a given cement content, statement (4) as a blanket claim is not generally correct; beyond an optimum, more sand reduces strength.

Step-by-Step Solution:
Accept (1): sand economizes cement usage.Accept (2): sand restrains shrinkage of the paste.Accept (3): by replacing paste volume, the exposed binder area to drying reduces; the statement reflects a standard rationale in mortar design.Reject (4): strength does not monotonically increase with sand; it depends on mix proportions and grading.

Verification / Alternative check:
IS mortar proportioning guidance shows optimum ranges for strength and workability; excessive sand lowers strength.

Why Other Options Are Wrong:

• Options that include (4) overstate sand’s effect on strength.

Common Pitfalls:

• Assuming more sand always increases strength; it usually reduces it past an optimum.

Final Answer:
1, 2 and 3 are correct