RESEARCH PAPER Chemo-mechanical behaviour of lightweight cemented soils E. Vitale 1 • D. Deneele 2,3 • G. Russo 1 • D. De Sarno 4 • M. V. Nicotera 4 • R. Papa 4 • G. Urciuoli 5 Received: 26 March 2018 / Accepted: 6 March 2019 Ó Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract In this paper, a multi-scale analysis of the effect of foam on chemo-mineralogical and microstructural features of the soil– cement–water system is presented. Time-dependent mineralogical and microstructural changes induced by foam were monitored at increasing curing times by means of X-ray diffraction, thermogravimetric analysis, scanning electron microscopy and mercury intrusion porosimetry. Addition of foam does not alter chemo-physical evolution of the soil– cement–water system in terms of either cement hydration or pozzolanic reactions. Large voids are present in the samples as footprints of air bubbles upon mixing, increasing the porosity of samples but not altering their matrix microstructure. Macroscopic behaviour of treated samples was investigated by direct shear tests. Chemo-physical evolution induced by adding cement is the main factor responsible for mechanical improvement shown by the treated samples. Sample porosity induced by adding foam plays a key role in the mechanical response of lightweight cemented samples, inducing a transition of stress–strain behaviour from brittle and dilative to ductile and contractile as foam content is increased. Keywords Cement Á Foam Á Mechanical behaviour Á Microstructure Á Soil treatment 1 Introduction One of the main problems encountered in constructing large port infrastructures is how to manage a very large amount of dredged material, especially if it has mechanical properties not suited to reuse as construction material. From the environmental and economic perspective, such material could represent an important resource if appro- priately worked and/or improved for re-use for construction purposes. A widely used solution for reusing dredged materials in port and harbour construction projects is to add cement and foam to produce lightweight cemented soil (LWCS) [10, 18, 19, 23–25]. LWCSs have been frequently used in Japanese coastal construction projects with the aim of reducing impact on underground structures (i.e. over- burden loads and lateral earth pressures) [15, 21, 22]. Kitazume and Satoh [11] successfully adopted this solution when constructing the Central Japan International Airport, treating soil by injecting cement and air into dredged sediments in the pipeline. Due to the turbulent flow, the mix formed by slurry and interspersed air bubbles facili- tates the transportability of the material and ensures the improvement of treated dredged sediments. The use of lightweight cemented soils has also been recognized as an effective material for building embankments on soft ground and other applications [9, 13]. LWCS is prepared by mixing air foam with natural soil, water and cement. The material is normally transferred by pumping from the batch plant to the construction site because of its high fluidity, and it is placed without com- paction. Effects of cement, foam and initial water content on unit weight and shear strength of LWCS have been thoroughly investigated elsewhere [5, 7], shedding light on the evolution of physical and mechanical properties as a function of treatment parameters. LWCS has low unit weight as well as moderate to high shear strength. Unit weight is typically between 6.0 and 15.0 kN/m 3 , mainly & G. Russo giarusso@unicas.it 1 Department of Civil and Mechanical Engineering, University of Cassino and Southern Lazio, Cassino, Italy 2 IFSTTAR, GERS, EE, 44344 Bouguenais, France 3 Institut des Mate ´riaux Jean Rouxel (IMN), Universite ´ de Nantes, CNRS, 2 rue de la Houssinie `re, BP 32229, 44322 Nantes Cedex 3, France 4 Department of Civil and Environmental Engineering, University of Naples Federico II, Naples, Italy 5 Terre Leggere S.r.l, Avellino, Italy 123 Acta Geotechnica https://doi.org/10.1007/s11440-019-00797-8