With the onset of summer in india and many parts of the globe construction personnel will need to take extra care or additional measures when it comes to concreting. In fact, some parts of the world remain hot throughout the year. These are situations when paying attention to a few simple yet very necessary points on hot weather concreting would certainly help in completing any concreting without compromising it’s quality. That’s what this article is about.
But, before proceding with soothing the trouble let’s throw a bit of sunlight in the trouble itself in order to understand what is it all about. Well, simply put, sunlight itself is the root of the whole issue. Sunlight leads to hot weather which compels us to adopt special measures while concreting which is known as hot weather concreting.
But then, what exactly is hot weather? The definition may vary from country to country. For Indian weather condition, Indian codes prescribe 40¤C as the threshold for hot weather concreting. That means, any concreting done at an ambient temperature of more than 40¤C can be regarded as hot weather concreting inviting special measures to be adopted.
Apparently, that’s not the case in many other parts of the globe due to different weather condition. For example, according to ACI 305, any combination of high ambient temperature, high wind, low relative humidity and solar radiation (sunlight) is a good enough pre-condition to label concreting as hot weather concreting. Some other views say that any temperature above a comfortable room temperature, say 25¤C or so, begins to make concrete bit uncomfortable ie, concrete starts reacting differently and hence calls for special care befitting hot weather concreting, if strict quality is to be maintained.
How is hot weather concreting different from concreting in normal temperature? We studied such things in great details in our engineering courses. To put it very simply & briefly, concrete sets and gains strength due to hydration of cement within it. Hydration of cement occurs faster in hot weather. Hydration of cement also releases heat. Hence, faster the hydration of cement faster the heat generation. This makes the concrete hotter, further speeding up the process of cement hydration or setting. Fast setting cement does not allow concrete enough time to gain strength sufficiently. While the initial strength may not suffer, the long term strength (28-day strength) is adversely affected. This is the key reason why hot weather concreting needs special care. Otherwise, you would be playing with the designed strength of the concrete.
But, that is not the only issue associated with hot weather concreting. Water demand of a concrete mix is higher in hot weather due to rapid evaporation. Unless suitable measures are adopted, extra water would have to be added to the concrete mix in order to maintain the workability of the mix. This would increase the water cement ratio which in turn would decrease the strength of the concrete. If additional cement is added to keep the w/c ratio unchanged then cost would increase as cement is the costliest ingradient of a concrete mix.
There are other problems too. Rapid drying of freshly poured concrete surfaces occurs in hot weather due to quicker evaporation or loss of water from the mix. If proper care is not taken this can lead to cracks known as plastic shrinkage cracks which are quite difficult to repair later on. Concrete surface tends to shrink quickly due to fast moisture loss while the mix is yet to develope sufficient strength to counter these shrinkage stresses resulting in the cracks.
In hot weather, the concrete bed, forms, steel reinforcement, mixing or concreting equipments etc. too get hot transferring the heat to the mix contributing further to the problem.
Based on my understanding on the subject which is based on some studies about the topic in books, the web as well as my practical experience on hot weather concreting in projects in India and the Gulf region, few important precautionary measures to be adopted while concreting in hot weather have been briefly discussed in the next post for the benefit of construction personnel and readers seeking a bit more info on the subject.
Contd. in Part II …..