Environmental Influences During Construction
See FHWA’s CRCP Design and Construction Guidelines for the references included in this page. A new, more comprehensive FHWA CRCP Design, Construction, Maintenance and Rehabilitation manual is currently under development and this page will be updated upon its release in the spring of 2016.
Climatic conditions such as ambient temperature, relative humidity, and wind speed during construction affect both crack formation and pattern in CRCP through a built-in thermal gradient and set temperature. Shrinkage and contraction stresses, which are the result of restrained movement caused by temperature and moisture changes and slab friction with base layers, cause cracks to develop at early ages. These cracks are likely to occur at an early age if the temperature rise of the concrete is not held to a minimum and the heat is not allowed to dissipate at a reasonable rate, or if the concrete subjected to a severe temperature gradient.
Hot Weather Conditions
Hot weather concreting is that when temperatures are above 90°F or 32°C. Particular concern exists when these condi- tions are accompanied by higher wind speeds and low rela- tive humidity. Concrete temperatures will generally be high as a result, and there is therefore an increased loss of water due to evaporation and an increased potential for early-age cracking. Early-age cracking due to hot weather tends to be wider than cracks that develop at later ages and can thus be more damaging to CRCP performance. In addition, rapid initial or false set may reduce the effectiveness of vibration in consolidating concrete around steel reinforcing bars.
Concrete Placement Time and Season
Early-age crack formation is related to both season and time of the day at which the concrete is placed. Recent CRCP studies in Texas indicate that concrete placed in warmer temperature experience more cracking over time and poorer crack pattern than concrete placed in cooler temperature. Also, concrete placed during daytime experienced crack formation much more quickly than concrete placed at night.(71) The FHWA HIPERPAV software can be used to identify the optimum time of day for paving to fit the current and forecasted environmental conditions to improve the performance of a CRCP. While night paving may not be desirable in urban areas (e.g., due to construction noise) the demonstrated improved performance and reduced conges- tion may help to justify paving at night.
Generally, CRCP placed in cool weather conditions performs better (longer crack spacing and smaller crack width) than CRCP placed in hot weather conditions. However, adverse weather conditions must be considered under these circumstances as well. Guidance provided in the IMCP Manual and elsewhere should be sought.