RELATIONSHIP BETWEEN SPECIFIC SURFACE AREA AND HYDRATION REACTION OF HARDENED CEMENT PASTE

ACP (amorphous calcium phosphate) and DCPD (dicalcium phosphate dihydrate, or Brushite) powders were high energy dry ball milled at a 1:1 ratio for 1, 2, 3, 4, 10, or 24 hours to produce a variety of powders for use as calcium phosphate cements (CPC). A 1:1 blend of powders not subjected to milling was used as baseline material (control). Physicochemical and mechanical characterization was performed on the powder or cement at each milling time point and compared to control. The following changes were noted after 24 hours of milling: the crystallinity was reduced to a fully amorphous phase, the tap density increased by 89%, the specific surface area decreased by a factor of 7, and the total porosity of hardened cement decreased by 50%. Additionally, the compressive strength of hardened CPC increased from 2.6 MPa to a peak of 50 MPa after 10-h milling. The rate of paste hardening increased throughout the 24-h period. Full conversion of each milled material produced a similar composition low-crystalline calcium deficiency apatite with Ca/P atomic ratio of 1.45 and specific surface area around 195 m2/g. The specific structure of these CPC, with high surface area and reactivity of nano-crystals, is ideal for in vivo remodeling of new bone and controlled release of protein and growth factors.

Download Full-text

Compressive Strength of Concrete with Nano Cement

Cement Industry - Optimization, Characterization and Sustainable Application ◽

10.5772/intechopen.93881 ◽

2021 ◽

Author(s):

Jemimah Carmichael Milton ◽

Prince Arulraj Gnanaraj

Keyword(s):

Compressive Strength ◽

Specific Surface ◽

Surface Area ◽

Specific Surface Area ◽

Cement Paste ◽

Cement Mortar ◽

Setting Time ◽

Replacement Level ◽

Initial Setting Time ◽

Initial Setting

Nano technology plays a very vital role in all the areas of research. The incorporation of nano materials in concrete offers many advantages and improves the workability, the strength and durability properties of concrete. In this study an attempt has been made to carry out an experimental investigation on concrete in which cement was replaced with nano sized cement. Ordinary Portland cement of 53 grade was ground in a ball grinding mill to produce nano cement. The characterization of nano cement was studied using Scanning Electron Microscope (SEM), Brunauer Emmett–Teller (BET), Energy Dispersive X ray microanalysis (EDAX) and Fourier Transform Infrared Spectroscopy (FTIR). From the characterization studies, it was confirmed that particles were converted to nano size, the specific surface area increased and the chemical composition remained almost the same. The properties of cement paste with and without nano cement were found. For the experimental study, cement was replaced with 10%, 20%, 30%, 40% and 50% of nano cement. Cement mortar of ratio 1:3 and concrete of grades M20, M30, M40 and M50 were used. Compressive strength of cement mortar and concrete with different percentages of nano cement was found. The cement mortar was also subjected to micro structural study. It was found that the strength increased even up to the replacement level of 50%. Further increase in the replacement is not possible since the addition of nano cement reduces the initial and final setting time of cement paste. At 50% replacement level, the initial setting time got reduced to 30 minutes which the least permitted value as per IS 12269: 2013. The increase in strength was due to the fact that nano cement acts not only as a filler material but also the reactivity increased due to the higher specific surface area. The SEM image shows the formation of additional C-S-H gel. The percentage increase in compressive strength was found to increase up to 32%. The workability of concrete with nano cement was found to be significantly more than that of the normal cement concrete.

Download Full-text