Most concrete contractors realize they eventually need to raise their prices if they're going to make a profit and survive in today's competitive marketplace. The question is whether you can raise prices without doing more harm to your business than good.
In a market where bid work is the norm, you can first test the waters to determine how your business volume will be affected by pricing. Your customers' behavior will then tell you when prices for your services are too high or too low.
There is no single indicator that a company's prices are too low. However, if your company has been suffering declining margins and eroding profitability, you certainly should raise prices. Most likely, the only consequence will be the loss of a few customers who wanted a lot for too little.