CCIL Advanced Aggregate Characterization 4

Question 1

Which accelerated chemical test per ASTM C1260 evaluates mortar bar expansion to assess potential alkali-silica reactivity (ASR)?

Accepted Answer

Mortar bar immersion in 1N NaOH at 80°C for 16 days

Answer

Concrete prism test at 38°C for 2 years

Answer

Chemical method measuring dissolved silica and alkalinity reduction

Answer

Petrographic examination of thin sections

Question 2

What expansion limit at 16 days in the ASTM C1260 accelerated mortar bar test is typically classified as potentially deleteriously reactive?

Accepted Answer

Greater than 0.10%

Answer

Greater than 0.05%

Answer

Greater than 0.20%

Answer

Greater than 0.50%

Question 3

The concrete prism test (ASTM C1293) is considered more reliable than ASTM C1260 primarily because it:

Accepted Answer

Uses actual concrete mixtures and measures expansion over 1–2 years

Answer

Produces results in fewer than 7 days

Answer

Measures chemical dissolution rather than physical expansion

Answer

Requires only coarse aggregate without cement

Question 4

Which deleterious substance in fine aggregate can interfere with cement hydration and is detected using the ASTM C40 colorimetric test?

Accepted Answer

Organic impurities

Answer

Chert particles

Answer

Lightweight particles

Answer

Clay lumps

Question 5

Alkali-carbonate reaction (ACR) in concrete differs from ASR because it primarily involves:

Accepted Answer

Dedolomitization of argillaceous dolomitic limestone aggregates

Answer

Microcrystalline quartz reacting with hydroxyl ions

Answer

Expansion of entrained air voids due to carbonate dissolution

Answer

Calcium carbonate precipitation in cement paste

Question 6

In petrographic analysis per ASTM C295, which preparation technique is most suitable for examining the microstructure and mineral grain boundaries of aggregate particles?

Accepted Answer

Polished thin section under transmitted and reflected light microscopy

Answer

Scanning electron microscopy without sample preparation

Answer

X-ray fluorescence bulk chemical analysis

Answer

Aggregate crushing and sieve size measurement

Question 7

Which mitigation strategy is most effective at suppressing ASR expansion when using a known reactive aggregate?

Accepted Answer

Incorporating sufficient supplementary cementitious materials to lower alkali availability

Answer

Increasing the water-cement ratio above 0.55

Answer

Using larger maximum aggregate size to reduce surface area

Answer

Adding calcium chloride accelerator to speed up hydration