ACI 546.2R-20 Guide to Underwater Repair of Concrete

ACI 546.2R-20 Guide to Underwater Repair of Concrete. 2.1—Defnitions ACI provides a comprehensive list of defnitions through an online resource, “ACI Concrete Terminology.” Defni- tions provided herein complement that resource. anti-washout admixture—chemical admixture that reduces the loss of fne materials from cement-based mate- rials when placed in water. tremie—a pipe extending below water, generally with a funnel-shaped top, through which concrete can be deposited. CHAPTER 3—CAUSES OF DETERIORATION 3.1—Introduction Concrete structures located in water are susceptible to various types of deterioration. The type and rate of deterio- ration depends on various factors including concrete proper- ties, reinforcing type, construction practices, and environ- mental conditions. Generally, structures located in warm marine (salt water) environments experience more rapid deterioration. In many cases, observed deterioration is the result of several deterioration mechanisms acting concur- rently (Holland et al. 2014). 3.4—Chemical attack Concrete under water is susceptible to deterioration caused by a wide range of chemicals. This deterioration may be clas- sifed as that caused by chemicals outside the concrete, and that caused by chemicals present in the concrete constituents themselves. In cases of external attack, the water frequently provides a continuous fresh supply of these chemicals. The water also washes the reaction products away and removes loose aggregate particles, exposing new concrete surfaces to further attack. Internal attack is accelerated by porous concrete, cracks, and voids. Alkali-silica reactions and corrosion of reinforce- ment are examples of internal attack. Internal deterioration also results when soluble constituents of concrete are leached out, resulting in lower concrete strengths and higher porosity. Splash-zone concrete is particularly susceptible to chem- ical attack because of the abundant supply of oxygen and frequent wetting-and-drying cycles caused by daily wave or tidal action, and temperature fuctuations. Chemicals present in water surrounding the concrete can cause deterioration that varies in rate from very rapid to very slow. The following are common forms of chemical attack. 3.4.1 Acid attack—Portland cement concrete is not resis- tant to attack by acids. In most cases, the chemical reaction between acid and portland cement hydration products, such as calcium hydroxide, results in the formation of water- soluble calcium compounds that are then leached away. ACI 201.2R and 515.2R describe acid attack in further detail. Symptoms of acid attack are loss of the cement paste and in severe cases, subsequent loss of coarse aggregate. If the acid has reached reinforcing steel, corrosion may be present.ACI 546.2R pdf download....