Mechanical and viscoelastic properties of cementitious materials using statistical analysis tools and nanoindentation

The research presents an investigation of mechanical and nanostructure characteristics of alternative cementitious materials such as blended and alkali-activated cements using nanoindentation technology and statistical analysis tools. Statistical analysis of these mechanical and nano characteristics of cementitious materials results in materials properties which are useful in structural engineering application. The indentation analysis shows that indentation properties such as modulus, hardness which are related respectively to elastic and strength properties with the projected area during the indentation loading and unloading process. With microporomechanics, the indentation modulus and hardness represents particle properties such as stiffness, Poisson’s ratio, cohesion, friction coefficient and packing density. The indentation analysis of cementitious material identifies the link between the multiphase compositions, and elastic, microstructure and viscoelastic properties. Statistical analysis tools are successfully being applied as a useful tool in studying the influence of parameters in cementitious materials. The results can be analysed using the ANOVA technique to examine the variation in the measured properties of cementitious materials. Moreover, the potential impact of indentation approach will encourage consideration of small scales examination to represent the large scale testing of civil engineering structural elements. Properties of hydration products of ordinary Portland cement (OPC) are determined as indentation modulus, hardness and packing density. The indentation modulus, hardness and packing density of LD CSH are 16.787 ± 4.804 GPa, 0.704 ± 0.144 GPa and 0.556 ± 0.01, respectively. The HD CSH has indentation modulus = 30.481 ± 4.257 GPa, hardness = 1.415 ± 0.222 GPa and packing density = 0.595 ± 0.001. Creep compliance rate of OPC shows that capillary pores phase is the main phase that tends to increase creep compliance. Also, indentation stress-strain curve shows that the strength failure can occur in capillary pore phase. Thus, porosity is an important factor to be considered when design OPC mixture. Based on statistic analysis of blended cements, an increase in fly ash content and sand to cementitious material ratio decreased the compressive strength development. The optimization of the compressive strength of blended cement mixture is found to be 20% of fly ash content, 1.5 of sand to cementitious material ratio, 0.35 of water to cementitious material ratio and 0.2% of superplasticiser. Similarly, alkali-activated fly ash cement (AAFA) was investigated based on statistical analysis tools and nanoindentation. The results show that the increase in sand has the greatest contribution to the increase in density. For compressive strength, normal paste without SF, sand and SP with l/s of 0.6 gives the highest strength and the increase in SF significantly contributes to the adverse effect on compressive strength. For the indentation data, the analysis using deconvolution technique confirms the four phases of reaction products of AAFA. The main phase is sodium aluminosilicate hydrate (N-A-S-H), which is over 40% of the volume fraction. The microporomechanics of AAFA paste and mortar also demonstrate the relationships between the N-A-S-H volume fraction and strength; and activation degree and strength. The creep behaviour of AAFA study revealed that partly-activated and non-activated phases are the main reason for creep due to “block-polymerisation” concept. It is also found that liquid to solid ratio is the most affecting parameter on creep, an increase of liquid to solid ratio leads to more creep.