RESEARCH PAPER Strength and stiffness of compacted chalk putty–cement blends Bruna Zakharia Hoch 1 • Andrea Diambra 2 • Erdin Ibraim 2 • Lucas Festugato 1 • Nilo Cesar Consoli 1 Received: 13 February 2021 / Accepted: 9 November 2021 Ó The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2021 Abstract Chalk breaks easily when subjected to human action such as mechanical handling, earthworks operations or pile instal- lation. These actions break the cemented structure of chalk, which turns into a degraded material known as putty, with lower strength and stiffness than the intact chalk. The addition of Portland cement can improve the behaviour of chalk putties. Yet, there are no studies determining the tensile strength of chalk putty–cement blends, the initial stiffness evolution during the curing time and other design parameters such as friction angle and cohesion of this material. This paper addresses this knowledge gap and provides an interpretation of new experimental results based on the dimensionless index expressed as the ratio between porosity and volumetric content of cement (g/C iv ) or its exponential modification (g/ C iv a ). This index aids the selection of the amount of cement and density for key design parameters of compacted chalk putty–cement blends required in geotechnical engineering projects such as road foundations and pavements, embankments, and also bored concrete pile foundations. Keywords Chalk putty Á Curing time Á Portland cement Á Stiffness Á Stress–strain–strength Abbreviations C 0 Effective cohesive intercept C Cement content (expressed in relation to mass of dry chalk putty) C c Coefficient of curvature C u Coefficient of uniformity C iv Volumetric cement content (expressed in relation to the total specimen volume) d Travel distance D 50 Mean particle diameter f Frequency G 0 Initial shear modulus G s Specific gravity G sec Secant stiffness modulus P 0 Effective mean stress q Deviator stress q t Splitting tensile strength q u Unconfined compressive strength R 2 Coefficient of determination T Wave period t p Travel time V s Wave velocity e s Shear strain e v Volumetric strain k Wave velocity q Soil specific mass c d Dry unit weight c s Unit weight of solids g Porosity g/C iv Porosity–cement index u 0 Effective friction angle & Nilo Cesar Consoli consoli@ufrgs.br Bruna Zakharia Hoch brunahoch@gmail.com Andrea Diambra andrea.diambra@bristol.ac.uk Erdin Ibraim erdin.ibraim@bristol.ac.uk Lucas Festugato lucas@ufrgs.br 1 Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil 2 Department of Civil Engineering, University of Bristol, Bristol, UK 123 Acta Geotechnica https://doi.org/10.1007/s11440-021-01415-2