**5. Conclusions**

This article describes exploratory experimentation on some of the properties of pastes and mortars made with different proportions of bentonite. The conclusions that may be drawn from the findings include the following.

	- a. In a sulfate solution for 56 d raises cement paste mechanical strength relative to the same materials stored in distilled water, attributed to greater age in the absence of expansive reactions;
	- b. Lowers the chloride diffusion coefficient significantly;
	- c. Reduces or maintains the carbonation depth observed in the reference material, deemed to be a very promising development.

New and innovative measures must be taken by the cement industry worldwide to minimise its impact on climate change. One effective approach to reaching carbon neutrality consists in using new constituents to manufacture Portland cement. Insofar as bentonite, while a clay material, calls for no thermal activation, the present authors suggest that it be classified under the European standard EN 197-1:2011 [50] heading 'natural calcined pozzolana (Q)'.

**Author Contributions:** Conceptualization, C.A. and J.A.T.R.; methodology, C.A.; experimental procedures, A.M.-S.; formal analysis, A.M.-S. and C.A.; research, C.A., A.M.-S., M.Á.S. and J.A.T.R.; writeup: original draft, C.A. and A.M.-S.; review and editing: C.A., A.M.-S., M.Á.S. and J.A.T.R.; supervision, C.A. and J.A.T.R. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Spanish Ministry of Science, Innovation and Universities under project ADIMULT [ref. BIA-2015-70350-R], and Spain's (Ministry of the Economy) training programme [ref. BES-2016-077157].

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data sharing is not applicable to this article.

**Acknowledgments:** Use of Eduardo Torroja Institute for Construction Science (a National Research Council body) facilities to conduct the study is gratefully acknowledged. The authors wish to personally thank L. Caneda-Martínez. M.I. Sánchez de Rojas, M. Frías and M.T. Blanco for their assistance with testing.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

