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2013FallShotcreteEMag

little to no moisture will be present during service significant to note that while certain workability life, or where only a mild threat of a chemical- characteristics may improve using coarser lime- attack environment exists, limestone “filler” stone fines, in general, overall durability replacements up to 15% appear to be acceptable. decreases.1,8,9,11,12,14 Again, this assumes that the portland cement and limestone combination has been “optimized.” Use in Wet, chemically This increased durability, in which little to no water contact or only mild chemical attack Aggressive exposures is likely, is due to the fact that increasing the When shotcrete is placed in a constant amount of limestone “filler” decreases the moisture/water contact environment, or where amount of cement, which, in turn, decreases the a moderate to severe chemical attack environ- amount of calcium hydroxide normally created ment exists, the overall durability of cement as cement hydrates. As the amount of calcium with limestone “filler” decreases with the hydroxide decreases, chemical deterioration increase in limestone (calcium carbonate). In associated with calcium hydroxide decreases. such environments, the combination of calcium And, while calcium carbonate formed hydroxide and calcium carbonate becomes more with limestone cements is also vulnerable to susceptible to attack, and accelerated deteriora- certain water-contact and chemical-attack tion of the concrete surface exposed to such environments, it is less vulnerable than conditions is reported. Limestone additions calcium hydroxide. Secondly, micro-fine lime- should not be allowed where the potential for stone has been shown to densify the paste sulfate attack (as is common in wastewater matrix (particle packing), reduce the gap—or treatment facilities or high sulfate soils), accel- distance between—the cement compounds erated chloride intrusion, or corrosion of rein- and sand/aggregate (the interfacial zone), forcement is a potential risk. Therefore, in and interact with the calcium aluminate shotcrete structures with constant moisture/ component of cement early on to form carboalu- water contact or where a moderate to minates, which are more stable in dry, nonag- severe chemical attack is likely to exist, the gressive environments.1,8-15 addition of limestone “filler” above 5% is Overall rheology (pumping, placing, and fin- not recommended. ishing ability) and workability of the material can Finally, as a helpful guideline, several be significantly enhanced using optimized micro- studies reported a correlation between the fine- fine limestone additions, which are reported to ness of the cement and limestone filler based decrease bleed, increase the adhesion of the mate- on the amount of limestone replacement. Based rial to the substrate, and increase cohesion of the on these reports, it is suggested that the current material itself. However, the opposite affect can accepted fineness requirement of bulk fineness occur as limestone fines increase in coarseness of under 45 microns (approximately 325 sieve greater than 45 microns (325 mesh). It is also or 3000 Blaine) and finer is not alone sufficient Table 2: Compression Strength of Market-Available White Portland Cement vs. White Limestone Cement Sample I.D. Type Date w/cm ratio 7-day 28-day 90-day White cement ‘A’, in. 2 x 2 cube 28-Aug-09 0.50 (s) 6181 7765 n/t White cement ‘B’, in. 2 x 2 cube 28-Aug-09 0.48 (s) 6529 8328 n/t White cement ‘A’, in. 2 x 2 cube 26-Oct-09 0.48 (s) 6333 8143 8455 White cement ‘D’, in. 2 x 2 cube 26-Oct-09 0.47 (lab) 6436 9879 10116 White cement ‘D’, in. 2 x 2 cube 28-Aug-09 0.52 (s) 6273 7838 n/t White cement ‘D’, in. 2 x 2 cube 10-Aug-10 0.54 (s) 6018 8275 8595 White cement ‘A’, in. with 15% limestone 2 x 2 cube 12-Jun-12 0.58 (s) 4374 5435 6096 White cement ‘A’, in. (‘parent’ cement) 2 x 2 cube 12-Jun-12 0.52 (s) 5614 6240 8211 White cement ‘E’, in. 2 x 2 cube 6-Sep-12 0.52 (s) 6791 7826 8499 White cement ‘D’, in. 2 x 2 cube 28-Aug-13 0.52 (s) 7204 9026 r/p Whie cement ‘B’, in. (‘parent’ cement) 2 x 2 cube 27-Aug-13 0.49 (s) 6234 9936 r/p White cement ‘A’, in. 2 x 2 cube 28-Aug-13 0.54 (s) 6706 8556 r/p White cement ‘B’, in. with 10% limestone 2 x 2 cube 28-Aug-13 0.52 (s) 5064 9301 r/p White cement ‘F’, in. 2 x 2 cube 27-Aug-13 0.54 (s) 5506 9184 r/p Note: n/t is not tested; (s) is field versus labw/c; r/p is results pending Shotcrete • Fall 2013 11


2013FallShotcreteEMag
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