You can try using chemical and physical methods. The recycled aggregate incrustation could be separated from the aggregate by washing in some adequate solution (take care when the aggregate is calcareous). A chemical analysis could be done to the separated material identifying the cement components. Some microscopy test could be use to support the interpretation and find a mass difference between cement and possible sand particles in the incrustation.

@Aria Tsam: The File or directory not found. :)

@ Luiz Pereira de Oliveira: I have know some chemical methods in ASTM or our national standard, but these methods just determine Na2O, SiO2 content in the solution of cement paste with adequate chemicals. I want to determine the ability of recycled concrete aggregates, which continuously hydrate when they replace natural aggregate in new concrete.

I have tested on mechanical of the consistent cement content in recycled aggregate by: grind recycled aggregate into powder with the fine as portland cement, and then use the powder to make mortar with silica sand (specimens with 40x40x160 mm). after 28 days curing in water, compressive strength of the mortar specimen reach 1,0 MPa. Do you have any comments on the test?

Dear Tong

This procedure is an indirect way to verify if the incrustation products on the aggregate are yet actives. When you talk that you have “tested on mechanical of the consistent cement content in recycled aggregate by: grind recycled aggregate into powder with the fine as portland cement, and then use the powder to make mortar with silica sand (specimens with 40x40x160 mm)”. It’s means that you are using the powders as cementitious materials in the mortar with silica sand. If is correct, the possible residual active products in the recycled aggregates incrustation is in large minority in the powder composition. It’s expected a very low compressive strength as you find. The ideal was to separate the incrustation products from the original aggregate and work with the paste phase, but this is quite impossible or at least not very practical. Perhaps, other way is using the powder as a mortar (eventual cementitious components + grinded aggregate). In this case you can find more “realistic” values. One thing is to verify if the eventual cementitious components in the recycled aggregate are or not active and other thing is quantify this contribution on mortar or concrete strength. The compressive strength data and microscopy of the recycled aggregate ITZ could help to interpret the potential benefits.

clinker containing high CaO, while aggregate content SiO2..by using XRF or XRD you will know what is the content CaO that may represent as clinker unless the aggregate also content CaO

I think statistical BSE imaging and analysis could be a good method for your purpose, but this method is complicated in sample preparation and data processing.

We made a machine to separate the attached old mortar from the virgin aggregate by grinding. The content of the cementitious hydrates can then be precisely determined. However, It is quite difficult to calculate the clinker content of the old mortar containing sand. DSC, XRD, IR can be used to investigate the potential hydration of RA.

LA test can also be used to test the clinker content when the  machine to remove the attached mortar by grinding is unavailable. First, establish the relation between LA loss and the real clinker content (obtained by soaking RA in HCl or sulphuric acid for 24 hours and calculating the mass difference before and after soaking); Second, run LA test and determine the clinker content.