Factors Causing Failures in Cement Concrete Pavements

Factors causing failures in Cement Concrete Pavements

These are recognized mainly by b y the formation of structural cracking. Failures are mainly due to two factors. I. Defi Defici cien ency cy of pave paveme ment nt mate materi rial alss II. II. Stru Struct ctur ural al inad inadeq equac uacy y of of the the pavem pavemen entt sys syste tem m I. Defi Defici cien enccy of pav pavem emeent mat mater eria ials ls Following are the chief causes which would wo uld give rise to the different defects or failures of cement concrete pavements. . Soft Soft aggr aggreg egat ates es !. "oor workma workmansh nship ip in #oin #ointt constr construct uction ion $. "oor #oint #oint fill filler er and and sealer sealer materi material al %. "oor "oor sur surfa face ce fin finis ish h &. Improp Improper er and and insu insuff ffici icient ent curing curing The various defects that creep in due to the above are

II.

. Disint Disintegr egrati ation on of of cemen cementt concr concrete ete !. Forma Formati tion on of crack crackin ing g $. Spal Spalli ling ng of #oin #oints ts %. "oor "oor ridi riding ng sur surfa face ce &. Slip Slippe pery ry surf surfac acee '. Formati Formation on of shrink shrinkage age cracks cracks (. Ingress Ingress of surfac surfacee water water and further further progressi progressive ve failures failures Struct Str uctur ural al inad inadeq equac uacy y of the pave paveme ment nt syste system m

Inadequate subgrade support pavement thickness would be a ma#or cause of developing structural cracking in pavements. Following are the causes and types of failures which develop. . Inadeq Inadequate uate pavement pavement thickne thickness ss !. Inadequate Inadequate subgrade subgrade support support and poor subgrade subgrade soil soil $. Incorr Incorrect ect spacin spacings gs of #oints #oints )bove would give rise to the failures of the following types . !. $. %. &.

*rack *rackin ing g of slab slab corne corners rs *racki *racking ng of pavemen pavements ts longi longitud tudina inally lly Sett Settle leme ment nt of of slab slabss +ideni dening ng of of #oi #oint ntss ,ud pum pumpin ping

Scaling of cement concrete

Scaling is observed in cement concrete concre te pavement showing overall deterioration of the concrete. The scaling is mainly attributed to the deficiency in the mi- or presence of some

chemical impurities which damage the mi-. Further due to the e-cessive vibration given to mi- the cement mortar comes to the top during construction and thus with use the cement motor gets abraded e-posing the aggregates of the mi-. This makes the pavement surface rough and shabby in appearance.

Shrinkage cracks

During the curing operation of cement concrete pavement immediately after the construction the shrinkage cracks normally develop. The placement of cracks are in longitudinal as well as in transverse direction. Spalling of joints

+hen pre/formed filler materials are placed during casting of pavement slabs the  placement is somehow dislocated and filler is thus placed at an angle. The concreting is completed without noticing this faulty alignment of the filler material. Thus this forms an overhang of a concrete layer on the top side and the #oint later on shows e-cessive cracking and subsidence. Warping cracks

If the #oints are not well designed to accommodate the warping of slabs at edges this results in development of e-cessive stresses due to warping and the slab develops cracking at the edges in an irregular pattern. 0inge #oints are generally provided for relieving the slabs of warping stresses. There is no structural defect due to the warping cracks if proper reinforcement is provided at the longitudinal and transverse #oints as it takes care of the structural adequacy. ud pumping

It1s recognized when the slurry e#ects out through the #oints and cracks of cement concrete pavement caused during the downward movement of slab under the heavy wheel loads. Following are the factors which cause the mud pumping. . 2-tent of slab deflection

!. Type of subgrade soil $. )mount of free water  "umping is noticed #ust after the rains in cement concrete pavements that are placed on clayey soil subgrade. Due to the application of repeated loads initial spaces are developed underneath the pavement. Since the soil is also of fine grained type it holds water and forms the soil slurry or soil suspension in water or the mud. Subsequent application of heavy wheel loads causes the pavement slab to deflect at critical locations and also forces out part of the mud each time through the spaces in pavement  #oints cracks or edge. +hen more and more mud is e#ected out there is a substantial loss in fine grained soil from subgrade resulting in considerable loss of subgrade support at these locations. +ith continued traffic movements there is progressive increase in the wheel load stress in the  pavement slab due to reduction in subgrade support consequently cracks are developed and the  pavement ultimately fails. The pavement cracking due to mud pumping is generally a  progressive type of failure in rigid pavements. Structural cracking

Inadequate pavement thickness for the amount and type of vehicles is the prime reason for the structural cracking. 3argely the pavements are found to crack at the corners and edges. 3ongitudinal and transverse cracks are also found to e-ist. It becomes quite difficult to differentiate the type of cracks. 4enerally if it could be decided that the crack in the vicinity of  #oints or corners are not due to spalling or mud pumping then the cracks are attributed to the structural inadequacy. The cracking in the interior regions are mainly due to the temperature stresses.