Carbonation of Cement Matrix

The alkaline pH of cement matrix can also be reduced by reaction between carbon dioxide (CO ) and Ca(OH. This reaction is known as carbonation of cementitious matrix and occurs in three stages (i) Initially CO diffuses in matrix through pores and is dissolved (ii) subsequently CO reacts with sodium hydroxide (NaOH) of cement matrix, decreasing the pH which favors Ca(OH formation and (iii) finally a reaction occurs between COj and Ca(OH that forms Ca(HCQ ) and CaCO. Several authors have used this reaction to decrease pH of cement matrix and increase durability of cement composites reinforced with natural fibers [31, 37, 69]. To allow this reaction occurs, composite is cured in an environment rich in COj, which favors the formation of CaCQ and therefore decreases the pH in the matrix [32, 70-73]. However, cement 

Toledo Filho et al. [32] conducted a comprehensive study to determine specific modifications of cement matrix and natural fibers that were effective increasing durability. Results indicated that carbonation of the specimens for 109 days at conditions of 26.5 C is a promising alternative for increasing the durabihty of cement composites reinforced with cellulosic fibers. 

2 Modifications of Natural Fibers to Increase Durability of Cement Composites 

Fiber Fiber Content Fibers Treatments Processing Technique Durability Test Results References 

Bagasse from sugar cane 0 - 20 wt% Soaked in water with a chemical admixture for 2 h. Casting pressure 2-3 MPa 25 wetting and drying cycles. Swelling 0.765% Water absorption T 16.45% Internal bond strength il4.5% [41] 

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