Can detrimental carbonation of cement or lime-stabilised road base layers, and the occurrence of biscuit layers as a result of carbonation, be controlled by proper construction techniques only?

• Published in: Journal of the South African Institution of Civil Engineers Vol. 60; no. 2; pp. 34 - 39
• Main Authors: Jooste, N.J.J, Semmelink, C.J, Raubenheimer, J.E
• Format: Journal Article
• Language: English
• Published: Johannesburg South African Institution Of Civil Engineering (SAICE) 01-06-2018; The South African Institution of Civil Engineers
• Subjects: Biscuit layer; Carbonation; Cement; Cementation; Civil engineering; Construction standards; Moisture; Organic chemistry; Ratios; Rehabilitation; Relative humidity; Road construction; Roads; Thin films; South Africa
• ISSN: 1021-2019; 2309-8775
• DOI: 10.17159/2309-8775/2018/v60n2a4

According to international standards, the majority of paved roads in South Africa are considered as low-volume roads. For this reason, the use of stabilised base layers under thin surfacings is still extensively used in the rehabilitation of these roads and the construction of new road pavements. In this spectrum of roads, problems have occurred with regard to the cementation of such layers. In most cases, these issues arise at the very top of these base layers, and the most common explanation has usually been described as “detrimental carbonation” or similar wording. It is especially the early problems within the construction period and soon thereafter that are under scrutiny in this paper. This paper presents an update on the experience with chemically stabilised base layers in South Africa, and shows how the so-called “detrimental carbonation” is not a situation that can be eliminated during construction. The paper further argues the reason why the problem is material-related, and that a water-driven reaction probably causes it. Other opinions are that carbonation is the only cause and that carbonation is unaffected by moisture. A further opinion is that standard prescribed compaction techniques, curing and the application of prescribed bituminous types of prime can also be the cause of so-called “detrimental carbonation”. The conclusion is that the problem is moisture or “water-driven”, as water vapour is required for the carbonation reaction to take place.