# One-Part Alkali-Activated Pastes and Mortars Prepared with Metakaolin and Biomass Ash
## 1 Introduction
[22] produced one-part geopolymers with BA as the precursor, by mixing rice husk ash, a silica-rich by-product obtained by calcination of rice husk at temperatures up to 800 \({}^{\circ}\)C, and anhydrous sodium aluminate with water at SiO\({}_{2}\)/Al\({}_{2}\)O\({}_{3}\) = 3.5 and Na\({}_{2}\)O/Al\({}_{2}\)O\({}_{3}\) = 1.0 molar ratios. They cured specimens in an oven at 80 \({}^{\circ}\)C and 80% relative humidity (RH) for different curing periods. They found that just 24 h curing is necessary to produce materials with a compressive strength of 30 MPa. The elevated mechanical properties of this type of one-part geopolymer were found to be related to the high degree of reaction of the silica and the absence of crystalline products (zeolites). Other authors used BA as the activator, without thermal pretreatment. For example, [PERSON] et al. [23] prepared white one-part AAMs by mixing dry powders at different NaOH/CaCO\({}_{3}\) molar ratios, composed of a calcium-rich wood biomass ash and NaOH, with diatomite, a siliceous sedimentary rock, and water. The obtained specimens were cured at 23 \(\pm\) 2 \({}^{\circ}\)C and 99 \(\pm\) 1% RH. The authors found that by decreasing the NaOH/CaCO\({}_{3}\) molar ratio of the dry activator, the compressive strength of the hardened one-part AAMs increased and the porosity decreased up to a certain limit; then the trend inverted for lower molar ratios. The highest compressive strength after 28 days of curing, 48 MPa, was obtained by one-part pastes manufactured with a NaOH/CaCO\({}_{3}\) molar ratio of 0.5 and was probably that high due to the nucleating sites and filling effects of CaCO\({}_{3}\). [PERSON] et al. [24] studied the possibility of using different types of potassium-rich BA as the alkaline activator to synthesize metakaolin-based one-part inorganic polymers. They found that a higher reactivity was obtained by maize cob ashes mixed with water and metakaolin with an ash/metakaolin (a/m) weight ratio of 0.9. Mortars were prepared with different a/m ratios, pressed at 59 MPa and cured with different procedures. The highest compressive strength (around 40 MPa) was obtained after pre-curing specimens at 20 \({}^{\circ}\)C for 24 h and then heating them at 80 \({}^{\circ}\)C for 48 h. [PERSON] et al. [25] produced one-part inorganic polymers with raw materials coming from Africa (Cameroon), by mixing metakaolin with a potassium-rich BA as the alkaline activator obtained by combusting cotton shells. Cotton shell ash was used as it is, and after calcination at 850 \({}^{\circ}\)C to improve its reactivity. They studied the evolution of hydration kinetics and compressive strength by varying the K/Al molar ratio of pastes and mortars. Moreover, they also compared the compressive strength of specimens only poured and vibrated with that of specimens with a lower water content but pressed at 7.9 MPa. They found that for both types of specimens, compressive strength values were increased by increasing the K/Al molar ratio. Moreover, when specimens were produced with pure cotton shell ash, one-part inorganic polymer mortars reached the highest compressive strength at a value of K/Al = 4; in the case of calcined cotton shell ash, the maximum compressive strength was obtained with a K/Al ratio of five, regardless of if poured and vibrated or compressed. The aim of this paper was to produce one-part alkali-activated pastes and mortars manufactured by adding only water to metakaolin and biomass ash coming from Europe, in order to see if the results obtained by [PERSON] et al. [25] can be reproduced by using different raw materials. The one-part alkali-activated mixtures produced in the present work were not subjected to compression, used instead for brick production, in order to evaluate if it is possible to manufacture a construction material that can be just poured in molds or applied as it is at the construction site without any additional treatment. Moreover, in the present experimentation a BA coming from wood has been used instead of one coming from agricultural waste.