Citovac

A Jeol JSM-IT100 scanning electron microscope (SEM) (JEOL Ltd., Tokyo, Japan) with a Bruker energy-dispersive X-ray spectroscope (EDS) (Bruker Corporation, Billerica, MA, USA) was applied for the analysis of the microstructure and healing products. Images were taken in the secondary electron mode (SED) and in the backscattered electron (BSE) mode. Test specimens for each mix were prepared and studied in the following way. After 21 days of healing, samples were dried in the oven for one hour at 45 °C and the crack surface was evaluated for the presence of healing products. In the next step, samples were broken in two halves through the crack and the crack plane was studied. In addition, one extra 12 month old UHPC specimen, U12, was cracked and studied after 1 and 21 days of water exposure. The chemical composition of the healing products and the amount of the unhydrated cement were determined by SEM-EDS analysis. Fragments of specimens A1, U1, and U12 were impregnated in epoxy resin, ground, and polished using Struers CitoVac and Labosystem (Struers, Ballerup, Denmark). A set of grinding plates sprayed with diamond particles having sizes of 9, 3, and 1 µm were used. The amount of the unhydrated cement was calculated based on the BSE image grey histogram by thresholding the white particles [44 (link)].

Vacuum impregnation was used for the soft ochre samples. The dried samples were put into mounting cup holders and then placed in a vacuum impregnation unit (Struers CitoVac). The mounting cups in the vacuum chamber were filled with impregnation material (EpoFix resin) under vacuum. Specimens impregnated with resin were then bonded onto a glass slide. Transmitted light microscopy and imaging was performed on polished thin sections using a Nikon Eclipse E600 POL microscope fitted with Nikon D90 digital camera.

CaP_Si scaffolds were impregnated with 10 w/v % PCL (M_n = 45,000, Sigma Aldrich) dissolved in the chloroform (CHCl₃, p.a. Kemika, Ovada, Italy) using the vacuum impregnation unit (CitoVac, Struers, Cleveland, OH, USA) as previously described in our research [11 (link)]. In brief, the porous CaP_Si scaffolds were put in a glass and placed in the vacuum chamber under a pressure of 0.11 bars. After 10 min at 0.11 bars, scaffolds were soaked in PCL solution for an additional 10 min. After impregnation, soaked CaP_Si scaffolds were placed on cotton fabric and then in the vacuum chamber at 0.11 bars for 10 min. The process was repeated in order to remove excess PCL solution and to dry the scaffolds. The composite scaffold preparation procedure is illustrated in Figure 1.