(NH4)2SO4 corrosion of cement in concrete analyzed by an improved mathematical model

Abstract

This paper gives a critical analysis of the equation that predicts and estimates the progress of degradation for various building materials, recently proposed by Matsufuji et al.1 After the analysis, the paper suggests an improved mathematical model, particularly for the modeling of sulfate corrosion. Experiments were performed with two samples of Portland cement and two samples of Portland cement with 30 % coal ash. The samples were immersed into a 10 % (NH4)2SO4 solution and the concentration of SO 2-4 in the solution and the material was measured. As a parameter that quantifies cement degradation, the quantity of bonded SO 2-4 was suggested. According to the obtained data, mathematical models for the description of sulfate corrosion were defined for all the examined samples. The models were applied for the analysis of the behavior of ash and non-ash containing samples. They allowed a better explanation of degradation which occurred during the investigated time period and even further they showed that ash systems were significantly more resistant to sulfate corrosion.

U radu je prikazana kritička analiza jednačine koja predviđa napredovanje degradacije raznih građevinskih materijala, a koju su u skorije vreme predložili Matsufuji i drugi. Posle analize, u radu je predložen poboljšan matematički model, posebno orijentisan ka modelovanju sulfatne korozije. Izvedeni su eksperimenti na dva uzorka Portland cementa i na dva uzorka Portland cementa sa 30 % letećeg pepela. Uzorci su potopljeni u 10 % rastvor (NH4)2SO4 i merena je koncentracija SO2-4 u oba sistema - rastvoru i materijalu. Kao parametar koji kvantifikuje degradaciju cementa uzet je sadržaj vezanih SO 2-4. Korišćenjem dobijenih podataka definisan je matematički model za opisivanje sulfatne korozije četiri ispitivana uzorka. Modeli su primenjeni za analizu ponašanja uzoraka sa letećem pepelom i bez njega. Oni omogućavaju ne samo bolju interpretaciju degradacije tokom ispitivanog perioda, već i pokazuju značajnu otpornost sistema sa letećim pepelom prema sulfatnoj koroziji.