Show a sample concrete mix design utilizing 100% CSA cement for precast countertops, detailing water

Here is a proven, high—performance mix design utilizing 100% Calcium Sulfoaluminate (CSA) cement for precast, cast—in—place, or Glass Fiber Reinforced Concrete (GFRC) backer/face coats for countertops.

Baseline Mix Formulation (Per 1 ft³ / ≈ 0.028 m³)

This formulation yields approximately 135–140 lbs (61–64 kg) of dense, workable mortar/concrete, sufficient to pour roughly 8 sq ft at 1.5 in thickness.

Critical Parameters

1. Water—to—Cement Ratio (w/c = 0.35—0.38)

• The Golden Rule of CSA: Unlike Portland cement, where lower water ratios (w/c < 0.30) are often pursued, CSA cement requires chemically bound water for the rapid synthesis of crystalline ettringite (C₆A S̄₃H₃₂).

• Lower Limit Warning: Never drop below w/c = 0.35. Sub—0.35 ratios cause severe autogenous shrinkage, curling, incomplete hydration, and matrix discoloration.

• Rely strictly on high—range PCE superplasticizers for flowability, not excess water.

2. Set Retarder Strategy: Citric Acid Only

• Incompatibility: Standard organic gluconate, tartaric, or lignin—based OPC retarders are ineffective or cause erratic set behavior in CSA binders.

• Mechanism: Foodgrade anhydrous citric acid acts as a calcium chelator, temporarily suppressing early ettringite precipitation.

• Pre—dissolve: Always dissolve granular citric acid thoroughly in the batch water prior to adding powder. Dry—blending can lead to unretarded flash pockets.

• Dosage by Temperature:

• 60℉—70℉ (15℃—21℃): 0.15%–0.25% by cement weight ≈ 20–25 min working time.

• 75℉—85℉ (24℃—29℃): 0.30%–0.45% by cement weight ≈ 15–20 min working time.

• > 85℉ (> 29℃): Requires ice/chilled batch water alongside 0.4%–0.5% citric acid.

Step—by—Step Batching & Mixing Procedure

1. Pre—Dissolve Liquids: Mix the entire volume of water (w/c = 0.36) with the weighed citric acid and liquid superplasticizer. Stir until completely dissolved and uniform.

2. Charge Dry Aggregate: Add sand and dry pigments (if using) into a pan mixer or high—shear bucket mixer.

3. Add Binder: Add the 100% CSA cement to the dry aggregate and homogenize for 30 seconds.

4. Wet Addition & Shear: Pour in the pre—blended liquid solution. Mix aggressively for 90 to 120 seconds until completely fluid and free of lumps.

5. Fiber Addition (If Applicable): Fold in AR glass fibers during the final 30 seconds of mixing at lower speed to avoid fiber degradation.

6. Cast Immediately: Place into pre—sealed, waxed forms without hesitation. Complete screeding and consolidation within 10–12 minutes of initial contact.

Mandatory Curing Protocol

CSA hydration is intensely exothermic and occurs within the first 60–180 minutes. The matrix actively demands water during this initial phase.

• Step 1: Immediate Vapor Seal (0 – 45 min):As soon as the countertop is finished and screeded, immediately cover the exposed back with heavy—gauge polyethylene plastic sheeting to prevent initial air draft evaporation.

• Step 2: External Wet Curing (1 – 4 hours post—pour):Within 45 to 60 minutes, the concrete will warm up significantly (40–50℃ core temperature), signaling rapid ettringite formation. Strip the plastic and apply a continuous external water source—either by wet burlap soaked in water, continuous fine misting, or ponding within perimeter forms. Maintain saturated conditions for a minimum of 3 to 4 hours.

• Step 3: Stripping & Processing (4 – 24 hours):Because CSA reaches roughly 3,500–5,000 psi (24–35 MPa) within 4 to 8 hours, demolding, edge polishing, wet grinding, and diamond processing can proceed the same day or early the following morning without edge breakout or corner chipping.