# Crushing Performance of Ultra-Lightweight Foam Concrete with Fine Particle Inclusions
## 2 Mixture Design and Sample Preparation  
A controlled sample without sand as well as nine mixtures of foam-sand composite samples of different sand ratio (mass ratio between sand and cementitious materials) and sand size were prepared for this study. The detailed information of the mixture design is given in Table 1, where the mixture naming convention is \"sand ratio_sand size\". The materials included cement (Essroc Italcementi Group, Type I/II), fly ash (Boral, Class C), water, superplasticizer (Sika, ViscoCrete 2100), an accelerator (Grace, Calcium Chloride 37), a foaming agent (BASF MasterCell 30), and river sand (specific gravity = 2.63). The \"300 um\" sand had a size range between 300 to 600 um, the \"600 um\" sand ranged from 600 to 850 um, and the \"850 um\" sand ranged from 850 to 1180 um. The foam concrete mixture design generally followed ASTM C796 [33], and the entire mixture preparation was divided into four steps: paste mixing, preparation of aqueous foam, foamed paste mixing, and sand inclusion. For preparing the paste, the mixing protocol followed the standard specified in ASTM C305 [34]. As part of the water was used for foaming, the water available for paste mixing was different across the samples. As such, the superplasticizer was used to maintain the same flowability of the fresh paste for the subsequent mixing. The accelerator was dosed as 8% by weight of cement for better stabilizing of the fresh foamed mixture [16]. A standard aqueous foam was prepared separately by blending water with the foaming agent at a 15:1 ratio. After that, the paste and foam were blended together using a high-speed mixer. During this step, different amounts of aqueous foam were progressively added to the mixture for achieving the target bulk density in different samples. The sieved sand particles were then gently poured into the foamed paste, after which the mixing was extended for 30 seconds to ensure an even final mixture. All the samples were designed to have the same bulk density of 0.55 g/cm\({}^{3}\). The paste in all samples was designed with 0.45 water-cementitious ratio (w/cm) and 40% fly ash replacement (by weight of cement). All liquid phase from the aqueous foam and chemical agents was considered for cement hydration when calculating the w/cm ratio. Considering the mixing process involves only using a portion of water for paste mixing, the cement created in the first step has a low w/cm ratio, down to 0.35. From previous experimental tests, mixing of this lower w/cm paste with the foam could not be blended into a homogenous mixture of foam concrete, even when dosed with a high amount superplasticizer. Therefore, a major portion of the cement was replaced with fly ash to obtain a more flowable paste mixture. Based on previous experimental work, it was observed the foam had void sizes ranging between 400 to 800 \(\upmu\)m. Therefore, the three sand sizes used in Table 1 were selected to differentiate the three cases that particles are smaller, within range, and larger than the voids. Since the density of the river sand is higher than the paste, the effective bulk density of the pure foamed paste decreases when the sand ratio increases (see Table 1). For each mixture, three prismatic specimens for the vibrational frequency test (50.8 \(\times\) 50.8 \(\times\) 203.2 mm) and three cylindrical samples for the penetration test (101.6 mm diameter by 203.2 mm height) were cast. The cylinder specimens were seal-cured in the mold until testing, while the prism specimens were demolded at 7 days and further cured under the sealed condition. The bulk density of each mixture was also measured at this age. Any sample that showed a deviation from the target bulk density larger than 0.05 g/cm\({}^{3}\) was rejected, and the mixture was recast. The bulk density of the accepted mixtures for testing is shown in Table 1.