🔹 1. Introduction

Expanding grout, also known as soundless chemical demolition agent (SCDA) or non-explosive cracking agent (NECA), is a controlled, non-detonating method of breaking rock and concrete.
Instead of using explosives, a special cement-based compound is poured into pre-drilled holes.
The compound expands as it hydrates, creating tensile stress within the rock until it cracks silently.This method is ideal for urban, underground, or vibration-sensitive environments where conventional blasting is restricted by DGMS or environmental laws.

🔹 2. Composition of Expanding Grout

Component	Function
Calcium oxide (CaO)	Main expansive agent (quicklime)
Silica / Alumina additives	Control expansion rate
Gypsum or retarders	Adjust setting time
Water	Hydration medium to trigger reaction

When mixed with water, the compound undergoes exothermic hydration, forming calcium hydroxide and expanding with tremendous pressure (up to 30–40 MPa).

🔹 3. Principle of Operation

1. Drill boreholes (32–50 mm diameter, depth 0.8–1 m typical).
   
2. Mix grout with water in a clean container (ratio per manufacturer).
   
3. Pour grout into holes immediately after mixing.
   
4. Within 2–8 hours, hydration causes slow but powerful expansion, exerting tensile stress on the surrounding rock.
   
5. The rock cracks and splits along the weakest planes without vibration, noise, or flyrock.
   

🔹 4. Advantages

• No vibration, flyrock, or shock – safe near structures.
  
• No license or explosive storage required (under DGMS norms).
  
• Low noise and dust, eco-friendly.
  
• Precise control – cracks follow drilled hole patterns.
  
• Usable indoors, tunnels, and populated areas.
  

🔹 5. Limitations

• Slower than explosives (hours vs seconds).
  
• Requires consistent borehole spacing.
  
• Effectiveness depends on temperature and water ratio.
  
• Unsuitable for massive, unfractured blocks without proper pattern.
  

🔹 6. Safety & DGMS Guidelines

• Use eye protection, gloves, and dust mask when mixing.
  
• Avoid direct contact — alkaline material may cause burns.
  
• Never look directly into filled holes.
  
• Allow proper reaction time before approaching cracked zones.
  
• Dispose of unused grout properly (never mix in confined spaces).
  
• Maintain job log of hole spacing, depth, temperature, and mix ratio.
  

🧠 . 25 DGMS-Style MCQs with Answers

1️⃣ Expanding grout is used mainly for —

a) High-energy blasting
b) Controlled, silent rock and concrete cracking
c) Generating seismic vibrations
d) Borehole priming
e) Tunnel detonation
✅ Answer: b) Controlled, silent rock and concrete cracking
Solution: It breaks rock chemically and quietly without detonation.

2️⃣ The main active component in expanding grout is —

a) Sodium nitrate

b) Calcium oxide
c) Potassium chlorate
d) Sulphur powder
e) Ammonium nitrate
✅ Answer: b) Calcium oxide
Solution: Quicklime reacts with water to form Ca(OH)₂, producing expansive pressure.

3️⃣ The typical hole diameter for grout application is —

a) 10–20 mm
b) 32–50 mm
c) 100–200 mm
d) 300–400 mm
e) >500 mm
✅ Answer: b) 32–50 mm
Solution: Medium-size holes allow enough grout volume for proper expansion.

4️⃣ Expanding grout cracks rock primarily by —a) Detonation
b) Rapid gas generation
c) Slow hydration and volumetric expansion
d) Electric discharge
e) Oxidation
✅ Answer: c) Slow hydration and volumetric expansion
Solution: The chemical reaction increases volume and internal stress.

5️⃣ The time for visible cracking after pouring grout is typically —

a) 5–10 minutes
b) 1–2 hours
c) 4–8 hours
d) 24 hours minimum
e) 3 days
✅ Answer: c) 4–8 hours
Solution: Depending on temperature, cracking occurs within several hours.

6️⃣ Which environmental condition increases expansion speed?

a) Low temperature (<10°C)
b) Moderate temperature (20–35°C)
c) Freezing conditions
d) Dry air without water
e) Acidic environment
✅ Answer: b) Moderate temperature (20–35°C)
Solution: Hydration reaction accelerates in warm, moist conditions.

7️⃣ The expansive pressure developed can reach —

a) 1–2 MPa
b) 5 MPa
c) 20–40 MPa
d) 100 MPa
e) <0.5 MPa
✅ Answer: c) 20–40 MPa
Solution: Enough pressure to fracture strong granite or concrete.

8️⃣ Safety PPE for grout handling includes —

a) Helmet, gloves, eye protection, and dust mask
b) Ear plugs only
c) Welding visor
d) Full blast suit
e) None
✅ Answer: a) Helmet, gloves, eye protection, and dust mask
Solution: Protects against splashes and dust burns.
9️⃣ The chemical reaction in grout is —

a) Combustion
b) Oxidation
c) Hydration (exothermic)
d) Polymerization
e) Dehydration
✅ Answer: c) Hydration (exothermic)
Solution: CaO + H₂O → Ca(OH)₂ + heat (expansion process).

🔟 Typical spacing between holes in hard rock is —

a) 0.1 m
b) 0.5–1.0 m
c) 5 m
d) 10 m
e) No pattern needed
✅ Answer: b) 0.5–1.0 m
Solution: Closer spacing ensures uniform cracking.
11️⃣ Expanding grout is also called —

a) Soundless Cracking Agent (SCA)
b) Liquid TNT
c) Slurry explosive
d) Blasting emulsion
e) Electric detonator
✅ Answer: a) Soundless Cracking Agent (SCA)
Solution: It works silently and without detonation.

12️⃣ DGMS classifies expanding grout as —

a) High explosive
b) Low explosive
c) Non-explosive chemical rock breaker
d) Detonating compound
e) Primer agent
✅ Answer: c) Non-explosive chemical rock breaker
Solution: It is chemical, not explosive, under DGMS classification.
13️⃣ The ideal water temperature for mixing grout is —

a) Ice-cold
b) 20–30°C
c) 50–70°C
d) Boiling
e) No limit
✅ Answer: b) 20–30°C
Solution: Ensures optimal reaction and expansion timing.
14️⃣ In winter conditions, setting time can be reduced by —

a) Heating holes slightly or using warm water
b) Adding acid
c) Freezing grout before use
d) Increasing hole diameter
e) Mixing longer
✅ Answer: a) Heating holes slightly or using warm water
Solution: Warmth accelerates the hydration reaction.
15️⃣ Expanding grout is best suited for —

a) Demolishing concrete structures in populated areas

b) Open-pit mass blasting
c) Coal seam shooting
d) Underwater mining
e) Slope stabilization
✅ Answer: a) Demolishing concrete structures in populated areas
Solution: Safe, quiet demolition where vibration control is critical.
16️⃣ The expansion process mainly generates —a) Acoustic waves
b) High-pressure steam
c) Chemical stress in confined holes
d) Compressed air
e) Magnetic fields
✅ Answer: c) Chemical stress in confined holes
Solution: Pressure develops inside holes, cracking the rock.
17️⃣ Grout should be poured within how many minutes after mixing?

a) 5–10 minutes
b) 20–30 minutes
c) 1 hour
d) 2 hours
e) Anytime after mixing
✅ Answer: a) 5–10 minutes
Solution: Mix sets quickly; pouring delay causes early stiffening.
18️⃣ Major precaution after pouring is —

a) Never look directly into the holes
b) Stir holes frequently
c) Add more water during reaction
d) Hammer holes to accelerate cracking
e) Cover holes tightly with metal caps
✅ Answer: a) Never look directly into the holes
Solution: Prevent eye injury from ejection due to expansion pressure.
19️⃣ Expansion generates internal pressure mainly due to —

a) Gas evolution
b) Volume increase during hydration
c) Combustion gases
d) External confinement
e) Elastic rebound
✅ Answer: b) Volume increase during hydration
Solution: Chemical reaction expands volume, producing internal pressure.
20️⃣ Common commercial names of expanding grout include —

a) Dynogel, Supergel
b) Bustar, Crackamite, Dexpan
c) Emulite, ANFO
d) Nitrogel, Cordtex
e) Nonel Tube, Primacord
✅ Answer: b) Bustar, Crackamite, Dexpan
Solution: Widely used international brands of SCDA.
21️⃣ Expanding grout exerts pressure of approximately —

a) 1 MPa
b) 5 MPa
c) 30–40 MPa
d) 100 MPa
e) 500 MPa
✅ Answer: c) 30–40 MPa
Solution: Enough to crack granite or reinforced concrete.
22️⃣ Hole depth should generally be about —

a) ¼ the block thickness
b) ⅔–¾ of the block thickness
c) Full depth of the bench
d) Half of borehole diameter
e) 2× block thickness
✅ Answer: b) ⅔–¾ of the block thickness
Solution: Provides adequate confinement for uniform cracking.
23️⃣ Improper mixing (too much water) results in —

a) Faster expansion
b) Reduced pressure and weak cracking
c) Explosive behavior
d) Color change only
e) Instant solidification
✅ Answer: b) Reduced pressure and weak cracking
Solution: Excess water dilutes reaction and lowers expansion pressure.
24️⃣ After reaction completes, the residue inside holes is —

a) Toxic and volatile
b) Harmless calcium hydroxide
c) Explosive residue
d) Sulfur compound
e) Nitrate-based fuel
✅ Answer: b) Harmless calcium hydroxide
Solution: Product is non-toxic lime (Ca(OH)₂).
25️⃣ Expanding grout technique is classified as —

a) Non-detonating chemical demolition
b) Explosive blasting
c) Air-gap blasting
d) Flame cutting
e) Electric fusing
✅ Answer: a) Non-detonating chemical demolition
Solution: It breaks rock chemically, not explosively.

                              🔚 8. Conclusion

Expanding grout provides a safe, silent, and vibration-free solution for rock and concrete demolition.
With proper drilling patterns, temperature control, and mixing procedures, it ensures precise cracking in restricted zones — fully compliant with DGMS-controlled operations where explosives are restricted.

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