PENGARUH JUMLAH DAN UKURAN AGREGAT PECAH TERHADAPKINERJA LAPIS PONDASI

Ir. H. Fakih Husnan, MM. MT,

Dosen Jurusan Sipil, Fak. Teknik Univ. Negeri Gorontalo

IntisariSpesifikasi Lapis Pondasi Agregat mensyaratkan batasan gradasi dalam bentuk amplop gradasidan nilai-nilai CBR. Pencampuran di Laboratorium antara sirtu dan agregat pecah untuk memenuhipersyaratan tersebut selalu dilakukan dengan perbandingan berat, sementara di lapangan umumnyadilakukan dengan perbandingan volume dan terkadang tidak memperhatikan amplop gradasi .Penelitian ini menguraikan hasil penyelidikan laboratorium terhadap tiga cara pencampuranmaterial agregat sebagai lapis pondasi antara sirtu alam dan agregat pecah dari beberapa ukuran yangsering diproduksi di pemecah batu untuk keperluan hotmix. Berbagai pengujian dilakukan terhadap bahanuntuk campuran seperti LAA, Nilai Setara Pasir, Indeks Kepipihan dan Kelonjongan, Berat Jenis, sedangterhadap kinerja campuran agregat dilakukan pengujian Pemadatan dan CBR.Hasil pengujian menunjukkan penambahan 20% sampai 40% agregat pecah ukuran No.4 – 1/2inci memperlihatkan peningkatan nilai CBR, selebihnya akan menurunkan nilai CBR. Penambahan 50%agregat pecah ukuran 3/8 inci - 1 inci meningkatkan nilai CBR tanpa rendaman sampai 86%, penambahanselanjutnya akan menurunkan nilai CBR karena diperkirakan tidak ada lagi friksi antara partikel agregathalus.Penambahan agregat pecah dengan ukuran No.4 – 1,5 inci memperlihatkan peningkatan nilainilaiCBR sampai 84% untuk kondisi tanpa rendaman, dan 81% dengan kondisi rendaman. Sebagaikesimpulan awal dari studi ini dapat dikatakan bahwa pembatasan nilai CBR 90% pada spesifikasi baruKimpraswil 2005 untuk LPA kelas A tidak dapat dicapai dengan cara pencampuran sirtu alam dan agregatpecah di lapangan.

AbstractThe specification of Aggregates Base Course requires a limitation grading in the form ofgradation envelope and CBR values. Mixing in the laboratory between natural sand and crushedaggregates to fulfill the requirement is always done by weight, meanwhile in the field it is generaly doneby volume and sometimes gradation envelope is neglected.This research outlines the results of laboratory investigation on three types of aggregatesmaterial mixing for base course layer of natural sand and various sizes of crushed aggregates oftenlyproduced in the stone crusher for hot mix purposes. A mixing based on by weight per fraction andgradation envelope limit was also done for the comparison purposes. Various tests were done to thematerials for mixture such as LAA, Sand Equivalent Value, Flakiness and Elongation Index, SpecificGravity, meanwhile for the aggregate mixtures were Compaction and CBR tests.The results show that natural sand and crushed aggregates were satisfied as a materials for basecourse material. The addition of 20% - 40% crushed aggregates of No.4 – 1/2 in. sizes shows theimprovement of CBR value. The addition of 50% crushed aggregates of 3/8 – 1 in. sizes improve the CBR

unsoaked value up to 86%, further addition will reduce the CBR value because maybe there are no morefriction between fine aggregate particles.The addition of crushed aggregates of No.4 – 1,5 in. size shows the improvement of CBR valuesup to 84% for unsoaked and 81% for soaked conditions. As a preliminary conclusion from this study canbe said that a limitation of CBR value of 90% in the new specification of Kimpraswil 2005 for class Aaggregate base course has not been achieved by mixing of sirtu and crushed aggregates in the field.Keywords : natural sand, crushed aggregate, aggregate base course, California Bearing Ratio