They provided good all-weather surfaces for the motor car, and were constructed using hot asphalt cements and cutback liquid asphalts. As cars and trucks became more popular and traffic loads increased, many of the chip-sealed roads were paved over with hot mix asphalt. Difficulties developed with the use of hot asphalt, such as rapid cooling and low adhesion qualities with dirty or wet aggregates. Slow curing became a problem with cutback liquid asphalts, and environmental and energy concerns also developed. Asphalt emulsions were created to solve these problems.
Asphalt emulsions are a mixture of asphalt cement, water, and an emulsifying agent.
Emulsions are easy to use, require low heating temperatures for spray applications, and most asphalt emulsions do not contain any petroleum distillates, which helps to alleviate environmental and energy concerns. After emulsions are sprayed, water starts to evaporate from the emulsion. Today, chip seals are primarily constructed with asphalt emulsions and polymer-modified asphalt emulsions. Also being used are polymer-modified asphalt cements and hot asphalt rubber compounds utilizing crumb rubber materials and asphalt cement. Only clean and well-crushed aggregates should be used on chip seals.