Timber/Lightweight Fill – Rendering sawdust chemically inert before use Before using sawdust as a lightweight filler or in non-structural composites, it can be rendered relatively inert by boiling it in water containing which additive?

Introduction / Context:
Organic fines like sawdust may interfere with cement hydration due to sugars and extractives, or may decay. Pre-treatment helps reduce harmful effects when sawdust is used in lightweight blocks, insulating plasters, or as filler in non-structural elements.

Given Data / Assumptions:

• Objective: reduce reactivity/leaching of organics from sawdust.
• Application in non-structural, low-strength composites.
• Simple, field-feasible chemical treatment.

Concept / Approach:
Boiling sawdust in a solution containing ferrous sulphate helps neutralize soluble tannins and sugars that retard cement hydration. The treatment precipitates some extractives and reduces biological activity, improving compatibility with cementitious matrices.

Step-by-Step Solution:
Select a salt known to complex with organic extractives → ferrous sulphate is commonly cited.Boil sawdust in the solution to leach and neutralize inhibiting compounds.Dry and use the treated sawdust in the intended non-structural mix.

Verification / Alternative check:
Materials handbooks list ferrous sulphate and similar salts for treating organic aggregates before mixing with cement to limit set-retardation.

Why Other Options Are Wrong:

• Potassium chloride/ammonia: not standard for this purpose in masonry composites.
• Nitric/sulphuric acid: strong acids are hazardous and can degrade cellulose, making them unsuitable in typical site practice.

Common Pitfalls:
Expecting structural performance from sawdust concretes; treatment improves compatibility but does not convert them into load-bearing materials.

Final Answer:
Ferrous sulphate