# Characterization and Reactivity of Natural Pozzolans from Guatema
###### Abstract  
The possibility of using pozzolanic materials as a partial substitute for Portland cement (PC) to develop mortars and concretes promotes environmental and economic benefits. The present paper includes an in-depth investigation into the characterization of natural pozzolans from Guatema for the valorization of these materials. An exhaustive physico-chemical characterization of the starting materials was first carried out. Second, an analysis of the pozzolanic reactivity of both pozzolans was performed using an evolution test of the pH and electrical conductivity measurements and a Frattini test. Finally, pastes and mortars were manufactured with pozzolans T and R as a substitute for PC. The results of the pH and electrical conductivity measurements confirmed that natural pozzolans can be classified as low-reactivity. The Frattini test and the thermogravimetric analysis confirmed the pozzolanic behavior of natural pozzolans at 28 curing days. In the cement pastes, lime fixation was positive for a long curing period, which demonstrated that these pozzolans had medium-long-term pozzolanic activity, similar to fly ash (FA). The results were confirmed by mechanical assays. The mortars with 15%, 25%, and 35% substitutions of cement for pozzolans had strength gain percentages of around 13-15% at 90 curing days. pozzolan; Frattini test; electrical conductivity test; compressive strength Article Characterization and Reactivity of Natural Pozzolans from Guatema  
[PERSON], [PERSON], [PERSON], J.  
earth, calcined clays, and shales) form a wide range of materials with pozzolanic properties that are commonly used as substitutes for cement clinker in mortars and concretes [6; 7; 8]. The fabrication of clinker to produce Portland cement (PC) generates about 8-9% of anthropogenic CO\({}_{2}\) emissions [9]. Manufacturing cements with lower clinker contents favors the reduction of cement-industry-derived emissions. In Europe, different types of cement are being manufactured, for which variable amounts of clinker are used and range from 94-80% clinker for type II/A cements to 20% clinker for type V/B cements. The latter may contain 31-49% natural pozzolans [10]. Different authors have studied using VP as supplementary materials [11; 12; 13; 14; 15]. [PERSON] et al. [11] investigated VP from Saudi Arabia and demonstrated that the binder's compressive strength decreased with a rising VP percentage. However, the binder with VP whose percentages ranged from 10% to 20% met the limits specified in ASTM C595 and ASTM C1157. [PERSON] et al. [14] studied a less common method of measuring reactivity. These authors examined reactivity following nano-indentation methods. They observed that a conversion of part of the C-S-H into C-A-S-H occurred when replacing cement with a natural pozzolan because of portlandite consumption. They also noted the distribution of unreacted pozzolan particles throughout the mixture with beneficial mechanical strength properties. [PERSON] and [PERSON] [15] employed VP at a proportion of 50% to fabricate self-compacting concrete. They demonstrated that the setting time increased as the VP percentage in the mixture increased, while the heat of material hydration decreased, which is an interesting aspect for large-volume mass concrete implementation. The concrete containing 50% VP reached 15 MPa after 28 curing days. This strength is sufficient for some applications. The chloride resistance was better in the mixtures containing VP because of pore refinement, which takes place due to the pozzolanic reaction. The consulted bibliography contains some articles that have employed materials deriving from volcanic activity as aggregates to manufacture mortars or concrete [16; 17]. In one of these research works, the authors pointed out that employing a fraction less than 0.5 mm for concrete manufacturing leads to positive results if the material is washed to eliminate any organic compounds present in volcanic materials [16].