Compressive Strengths of Cube vs. Cored Specimens of Cement Stabilized Rammed Earth Compared with ANOVA  
[PERSON]  
1 Faculty of Civil Engineering, Warsaw University of Technology, Al. Armil Ludowej 16, 00-637 Warsaw, Poland; 1 [EMAIL_ADDRESS] (L.R. ); [EMAIL_ADDRESS] (P.N. )1  
[PERSON]  
1 Faculty of Civil Engineering, Warsaw University of Technology, Al. Armil Ludowej 16, 00-637 Warsaw, Poland; 1 [EMAIL_ADDRESS] (L.R. ); [EMAIL_ADDRESS] (P.N. )1  
[PERSON]  
1 Faculty of Civil Engineering, Warsaw University of Technology, Al. Armil Ludowej 16, 00-637 Warsaw, Poland; 1 [EMAIL_ADDRESS] (L.R. ); [EMAIL_ADDRESS] (P.N. )1  
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laboratory-molded specimens. The absence of international standards for CSRE highlights the need for multicriteria material assessments, as unconfined compressive strength (UCS) alone may not sufficiently describe the material's mechanical properties [9]. For CSRE, there is little correlation between the compressive strength of laboratory specimens and finished construction elements. Singular studies comparing the strengths of rammed and cored cylinders found the difference to be negligible (around 2%) [10]. Such correlations are crucial for the safe design of buildings using this eco-friendly material. Similar experimental investigations have been documented in the literature [11]. Researchers have found significant differences in strength between molded and cored specimens, with molded specimens generally exhibiting higher mechanical strength. Specimens compacted in small molds typically have higher strength than wall elements. The compressive strength of CSRE was typically tested after about 28 days of specimen curing, as documented in references [10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30], analogous to concrete testing according to EN 206 [31]. For concretes with Portland cement (CEM I), compressive strength after 28 days is only slightly lower than the maximum value. However, for other types of cement, such as blast furnace cement (CEM III) or multi-component cement (CEM V), strength increases over a much longer period of time. Thus, concretes using CEM III and CEM V are often tested after longer curing periods, such as 56 days, 90 days, or more, to assess compressive strength accurately. For CSRE, the unfired clay in the soil slows down the setting of Portland cement, resulting in a longer period of strength increase beyond 28 days. In the article [32], the UCS of the CSRE specimens showed that at 60 days of curing, the strength of the cube specimens was between 109% and 125% of their strength at 30 days; at 90 days, the strength ranged from 110% to 135% of the 30-day strength; and at 120 days, the strength was between 110% and 140% of what it was at 30 days. Additionally, the strength of non-stabilized rammed earth walls has been shown to increase with drying over time, well beyond the 1-month period [33]. Moreover, raw earth consists of numerous minerals that slow down the development of compressive strength in CSRE, primarily due to the deceleration of the hydration process of cement [29; 30]. Therefore, it is reasonable to assume that the compressive strength of CSRE continues to develop significantly even after 28 days. To test this hypothesis, destructive tests should be conducted after extended periods. In research [28], the impact of the shape and size of CSRE specimens on compressive strength was investigated (Figure 1). Specimens were tested with 10% and 20% cement contents. They were cured in high-humidity conditions for 28 days and, after this period, dried for 10 days at ambient temperature. The obtained results are shown in Figure 2. It was demonstrated that compressive strength decreases with increasing size.