The Experimental Study On Microbial Induced Carbonate Precipitation To Repair Concrete Cracks

As the most widely used construction material, the concrete leakage problem after cracking is always a problem in engineering. The leakage problem can affect the durability and water impermeability of concrete structures and reduce the bearing capacity. There are many repair methods of concrete crack until now, but most of them have shortcomings such as poor bonding power, poor durability and causing environmental pollution.With the development of engineering technology, microbial induced calcium carbonate precipitation technology gradually become the focus of researchers. It can use urease produced by microbial metabolism to decompose urea. The carbonate ions produced by urea decomposition and calcium ions in the environment can be combined to form calcium carbonate. With increasing deposition of calcium carbonate in the cracking sites, concrete cracks will be eventually remediated.The experiment used Bacillus pasteurii induced calcium carbonate precipitation to repair concrete cracks. The repair effect was tested by setting different factors and impermeability experiments. The main contents and conclusions are as follows:1. The changes of early calcium formation rate was studied when urea was added to the bacteria solution in advance. The results show that the early calcium formation rate can be improved significantly when urea was added to the bacteria solution in advance.2. The bacterial activity is the main factor that affect plugging rate. When the bacterial activity is high, many calcium carbonates will be produced and the plugging rate become faster than before.3. The influence of different factors (crack width, crack depth, mediums, calcium sources) was studied on plugging concrete cracks with Bacillus pasteurii. The results showed that the four factors affecting plugging rate in a descending order as:crack width, crack depth, mediums and calcium sources. Other things being equal, the plugging rate will be faster if cracks are narrow and deep meanwhile mediums were packed in the wide cracks. Calcium acetate or calcium nitrate can be selected as calcium sources which have no corrosion harm of reinforced.4. The impermeability of concrete cracks after bioremediation was studied by impermeability experiments. The results show that most of the concrete cracks have good impermeability after plugging by Bacillus pasteurii. The crack width and crack depth are the important factors that affect the impermeability after bioremediation. Other things being equal, it will have good impermeability if cracks are narrow and deep meanwhile mediums were packed in the wide cracks.5. According to the theory of plugging concrete cracks with Bacillus pasteurii, it’s easy for calcite crystals to be caught, bridged and deposited when the crack width is small. The deep crack means that the chance of bridging and depositing will be increased because distance and time are long when calcite crystals flow through the cracks. Cracks can be divided into smaller pieces and the friction force will increase when mediums were packed in the wide cracks. It will have good plugging rate and impermeability if cracks are narrow and deep meanwhile mediums were packed in the wide cracks.