Calculate required liquid asphalt volume or verify application rates.
MATERIAL ESTIMATION
VERIFICATION (OPTIONAL)
Total Surface Area:0 yd²
Required Prime Coat:0 Gallons
ACTUAL ACHIEVED RATE:0.00 gal/yd²
Difference from Target:0.00%
function calculatePrimeCoat() {
// Get Inputs
var lenStr = document.getElementById('roadLength').value;
var widStr = document.getElementById('roadWidth').value;
var rateStr = document.getElementById('targetRate').value;
var usedStr = document.getElementById('gallonsUsed').value;
// Parse Inputs
var length = parseFloat(lenStr);
var width = parseFloat(widStr);
var targetRate = parseFloat(rateStr);
var actualGallons = parseFloat(usedStr);
// Validation
if (isNaN(length) || isNaN(width) || length <= 0 || width 0) {
actualRate = actualGallons / areaSqYd;
hasActual = true;
}
// Display Results
document.getElementById('resArea').innerHTML = areaSqYd.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}) + " yd²";
if (!isNaN(targetRate)) {
document.getElementById('resGallonsNeeded').innerHTML = gallonsNeeded.toLocaleString(undefined, {minimumFractionDigits: 0, maximumFractionDigits: 0}) + " Gallons";
} else {
document.getElementById('resGallonsNeeded').innerHTML = "–";
}
// Display Verification Rows if data exists
var verifyRow = document.getElementById('verifyRow');
var diffRow = document.getElementById('diffRow');
if (hasActual) {
verifyRow.style.display = 'flex';
document.getElementById('resActualRate').innerHTML = actualRate.toFixed(3) + " gal/yd²";
if (!isNaN(targetRate) && targetRate > 0) {
diffRow.style.display = 'flex';
var diffPercent = ((actualRate – targetRate) / targetRate) * 100;
var sign = diffPercent > 0 ? "+" : "";
document.getElementById('resDiff').innerHTML = sign + diffPercent.toFixed(2) + "%";
document.getElementById('resDiff').style.color = (Math.abs(diffPercent) > 5) ? "red" : "green";
} else {
diffRow.style.display = 'none';
}
} else {
verifyRow.style.display = 'none';
diffRow.style.display = 'none';
}
document.getElementById('pcResult').style.display = 'block';
}
Understanding Prime Coat Spray Rates
In asphalt paving and civil engineering, Prime Coat is an application of low-viscosity liquid asphalt to an absorbent surface, such as a crushed stone base or stabilized soil. The primary purpose of calculating the correct spray rate is to ensure the material penetrates the base sufficiently to bond the underlying layer to the new asphalt overlay, without creating a slippery, unabsorbed film (bleeding).
The Importance of the Correct Spray Rate
Applying prime coat at the correct rate (measured in gallons per square yard or liters per square meter) is critical for structural integrity:
Too Light: The asphalt layer may not bond to the base, leading to slippage cracks or delamination.
Too Heavy: Excess asphalt can migrate upward into the new pavement, causing instability, rutting, or flushing (shiny spots on the road).
Typical Application Rates
The ideal spray rate depends heavily on the "tightness" or porosity of the granular base material.
Tight Surface (low porosity): 0.20 to 0.30 gal/yd²
Average Surface: 0.30 to 0.40 gal/yd²
Open/Loose Surface (high porosity): 0.40 to 0.50 gal/yd²
Always refer to local DOT specifications or the project engineer's requirements.
Formulas Used in Calculation
To determine how much material is required, or to verify the rate applied by an asphalt distributor truck, we use the following formulas:
Area (yd²) = (Length (ft) × Width (ft)) ÷ 9
Total Gallons Required = Area (yd²) × Target Rate (gal/yd²)
Actual Spray Rate = Gallons Used ÷ Area (yd²)
Example Calculation
Suppose you are priming a road base that is 1,000 feet long and 12 feet wide. The specification calls for a rate of 0.35 gal/yd².
Calculate Area in Square Feet: 1,000 × 12 = 12,000 sq ft.
Convert to Square Yards: 12,000 ÷ 9 = 1,333.33 yd².
If the distributor truck sprays the entire section and uses 500 gallons, the actual rate was:
500 ÷ 1,333.33 = 0.375 gal/yd² (slightly heavier than target).