Investigation of the hydration of clinker-reduced cementitious binders by 1H NMR relaxometry

Abstract In this paper, we demonstrate the value of $$^{1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mn>1</mml:mn> </mml:mmultiscripts> </mml:math> H NMR relaxometry for studying the hydration of clinker-reduced, climate-friendly cementitious binders. Our study includes white cement (WC), ordinary Portland cement (OPC), and samples incorporating reactive agro-waste based ashes and non-reactive biochars as supplementary cementitous materials (SCM). NMR measurements were performed over a period of up to 120 h during hydration with an echo time of 50 $$\upmu$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>μ</mml:mi> </mml:math> s and a relatively large sample size of 20 mL. The results were compared to heat flow calorimetry (HFC) data, and a detailed comparison with literature data was performed for pure OPC and WC. The results show that time-resolved NMR measurements, especially the analysis of individual NMR signal components assigned to defined $$^{1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mn>1</mml:mn> </mml:mmultiscripts> </mml:math> H reservoirs, are effective for studying hydration processes. They offer insights into the evolution of the microstrucure and specific chemical phases. NMR provides valuable information and serves as a good complement to HFC. The comparison with data obtained with shorter echo times (40 $$\upmu$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>μ</mml:mi> </mml:math> s or around 15–45 $$\upmu$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>μ</mml:mi> </mml:math> s with solid echo sequence) on much smaller samples showed almost identical developments with respect to the $$\hbox {T}_2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mtext>T</mml:mtext> <mml:mn>2</mml:mn> </mml:msub> </mml:math> distributions. For the SCM samples, NMR results indicated partially accelerated hydration processes compared to classical OPC hydration. One SCM sample acted as a highly reactive pozzolan, showing a similar hydration process to OPC with the strongest effect observed when superplasticizer was added. Adding biochar delayed C-S-H gel pore formation but significantly increased capillary pores and even free water, likely due to the sponge-like structure.