Applications of the Maturity Method

A technique, which takes into account the combined effects of time and temperature on the strength development, is called maturity method. This method can be used to predict in-place strength of concrete to make sure that critical construction schedule, such as formwork removal, applied post-tensioning, can be implemented safely[101, 106].

There were fourteen workers killed and 34 injured in an accident of the collapse of a multi story building, under construction in Fairfax County, Va., in March 1973. The National Bureau of Standards (NBS) reported that the most probable cause of the collapse was premature removal of formwork[4]. In April 1972, another building collapsed, which is being constructed in Willow Island, WV. The accident resulted in 51 workers death. The NBS reported that the most likely cause of the accident was insufficient concrete strength to support the applied construction load[106]. Since the accidents, the NBS researchers started an in-depth study of the maturity method. As a result they laid the foundation for the advance of the first standard in the world for the maturity method i.e. ASTM C-1074. Maturity method has been used for more than 3-decades on many constructions for prediction the strength of concrete[144]. An accurate predicted strength, enable engineer to reschedule the time of construction. Therefore, it can save a considerable amount of construction time, and it might be used as a tool in scheduling construction activities.

Waller et al[167], reported that in practice, the maturity method involves three phases such as calibration, validation and an on-site application. The calibration phase consist of the measuring of the expected properties of the given concrete mixture, such as the compressive strength, the estimated maximum temperature of concrete, and finding the suitable value of apparent activation energy. This phase leads to the development of the “concrete calibration curve”, where the curve was obtained from the expected development of the strength of vs. maturity at 200C.

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The validating phase occurs during the first week of the project. This phase is to check whether the variations in the characteristics of the concrete do not have significant difference to that of used in calibration phase. If there is no significant

differences from those are used in calibration phase, therefore, the “calibration curve” could be used as the ‘reference curve’ on the project. Finally, the on-site application phase, it continues throughout the project where it is necessary a regular checking of the characteristics of the concrete.

Furthermore, Waller at all reported the use maturity method successfully for over than 20 years in Europe on many different projects in Europe, especially for assessing the early age strength of concrete as shown in Table 2.3.

Table 2.3: Lists some projects used the maturity method successfully to predict the strength of concrete at early ages, in Europe

Project Year location

Pylons and deck segments of Normandy bridge 1991 France[167]

“Pas de l'Escalette” tunnels A75 1994 France[167]

Cantilever deck segments of Rhone Viaduct BPNL 1994 France[167] Cooling towers of Civaux nuclear plant 1994 France[167] Rochecardon and Duchère tunnels BPNL 1995 France[167]

Montjézieu tunnels A75 1995 France[167]

Mirville viaduct A29 1995 France[167]

Amiens PI4 viaduct 1995 France[167]

Precast segments of “Ile de Ré” bridge 1987 France[167]

TGV viaducts in Avignon 1997 France[167]

Cut and cover in Taverny A115 1997 France[167]

Nièvre viaduct A16 1998 France[167]

Lisieux PI5 viaduct 1998 France[167]

Channel tunnel rail link, Medway bridge 2000 UK[167]

Table 2.4 presents some of the project those used the maturity method to estimate the strength of concrete that used in the projects at early ages.

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Table 2.4: Lists some projects used the maturity method successfully to predict the strength of concrete at early ages, in the USA and Canada

Project Year location

Scotia plaze 68-story tower 1986 Canada[168]

Creve Coeur Lake Memorial Park Bridge - US[169]

Barnes Hospital parking garage 2001 US[169]

Kiefer Creek Overpass - US[169]

Residential 30-story tower 2001 US[169]

Interstate 40 bridge reconstruction- Oklahoma 2002 US[169]

Roy et al[170] reported on the use of the maturity method during two projects. They used commercial software, which is called Computer Interactive Maturity System (CMIS) to calculate the heat and strength development. In this software, it is assumed that the relationship between the heat and maturity, and the strength and maturity is an exponential. Two projects were chosen to evaluate the CIMS model. The first project was a central bridge pier, which was placed on a foundation in the middle of Clearfield Creek. The second project was a Highway Slab. The results showed that the predicted temperatures in the concrete were the same trend to that of observed in the field. However, the predicted strengths need further verification in order to obtain an accurate result.

In 1999, Pinto and Hover[171] studied the effect of temperature on the setting times of concrete, using the maturity approach and FHP equation (Equation 2.13). They concluded that the setting time could be used to estimate the apparent activation energy successfully at the early stages of hydration. While the maturity method could be used to estimate the variations I setting times due to different curing temperatures.

In 2004, Schindler[172] observed the effect of temperature on the initial and final setting times of concrete mixtures. It was quite similar to that of Pinto and Hover did. However, Schindler also observed the effect of the use of different cements and supplementary cementitious materials on the initial and final setting times of

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concrete. He found that the setting time of concrete with Portland cement only was accurately predicted. However, when GGBS is used in concrete, setting occurs at an earlier degree of hydration. For this reason, he recommended that the interaction between the setting time and the hydration of GGBS needs to be further investigates.

More recent, Han et al[173] investigated the use of maturity method to predict the setting time of concrete incorporating with super retarding agents (SPA). They concluded that the maturity method could be used to predict the setting time of concrete containing SPA, where the results showed a good agreement between the predicted setting time and the measured setting time.

In 2009, Anderson et al[174] used the maturity method on the three case studies on actual construction projects. The three projects were all paving projects in the state of Washington. One of them, was a complete rebuild of a section I-5 in downtown Seattle, while the other two panel replacement, where one on I-5 in Bellingham and the other one on I-205 in Vancouver.

They found that the maturity method is a useful tool for estimating the strength development of the pavement. Proper understanding and use of maturity method results in a reasonable good of strength prediction, thus enables contractors to increase their productivity on projects with accelerate the construction schedule. On all their case studies, there was a lack of compliance with the special provision; such as no verification testing, inadequate recording keeping and in one case a calibration curve was not valid. Furthermore, they also reported the weaknesses of the maturity method, such as when there was a change in brand of cement, the source of type of cement of other cementitious materials, the source of aggregate and water-cement ratio; the strength-maturity relationship, therefore, required a new calibration curve.

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